Plugins breaking: Convert all synchronous interface methods to Task

Okay, I wish we had uncovered it earlier as part of V5.2 but it has bitten us in the back just now, so I'm addressing it as part of monthly cycle instead.

Previously used void methods did not allow async operations in plugins in a "nice way". If plugin didn't require synchronization with the ASF and just minded its own business, it wasn't half bad as it could use async void signature. However, if plugin by any chance had to do something BEFORE ASF continued with the rest of the logic, it had to explicitly leave non-async void signature and call its async-capable stuff in synchronous manner (usually with Wait() or .Result), which is vastly suboptimal.

This was visible even in our STD plugin, which previously had (and still has) GlobalCache initialization in OnASFInit(). If that cache initialization took a bit longer time, STD would hit InvalidOperationException() in OnLicenseList() callback as global cache didn't load yet while we were already long past OnASFInit().

Therefore, I've decided to make a breaking change for a very good reason - all previous methods were converted to tasks, which allows from plugin to do one of three things:

- If plugin is async and requires synchronization (like STD), it can declare itself as async await, and do its awaits as-needed, and ASF will wait for those.
- If plugin is truly synchronous (and not just a synchronous signature with awful Wait() or .Result, see above), it can simply return Task.CompletedTask and has exactly the same logic.
- Finally, if plugin calls some async stuff but doesn't need ASF synchronization, it can "offload" itself from it by calling e.g. ASF's Utilities.InBackground() with whole logic, while returning Task.CompletedTask from the main method. This will allow it to effectively do what async void previously did, by just hooking into the process without intention of slowing it down.

All in all I'm confident this approach, while a bit counter-intuitive at first, will result in better compatibility between ASF and the plugins, as if I wanted to fix my STD issue right now without that breaking change, I'd have to actually call .Result on my async global cache loader function, which is utterly stupid if we can fix ASF to do the right thing instead.

This "approach" can be commonly found in some other libs with similar to ASF's event-hook behaviour, e.g. Discord.Net.

You'll sadly need to do some method signature changes in all of your plugins, as the core OnLoaded() was also changed. See the ones I did in SteamTokenDumperPlugin.cs if you need a practical example, and see ExamplePlugin.cs if you need further explanation.

ArchiSteamFarm.OfficialPlugins.SteamTokenDumper/SteamTokenDumperPlugin.cs

@@ -62,7 +62,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 
 	public Task<uint> GetPreferredChangeNumberToStartFrom() => Task.FromResult(Config?.Enabled == true ? GlobalCache?.LastChangeNumber ?? 0 : 0);
 
-	public async void OnASFInit(IReadOnlyDictionary<string, JToken>? additionalConfigProperties = null) {
+	public async Task OnASFInit(IReadOnlyDictionary<string, JToken>? additionalConfigProperties = null) {
 		if (!SharedInfo.HasValidToken) {
 			ASF.ArchiLogger.LogGenericError(string.Format(CultureInfo.CurrentCulture, Strings.PluginDisabledMissingBuildToken, nameof(SteamTokenDumperPlugin)));
 
@@ -100,8 +100,6 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 			config.Enabled = true;
 		}
 
-		Config = config;
-
 		if (!config.Enabled) {
 			ASF.ArchiLogger.LogGenericInfo(string.Format(CultureInfo.CurrentCulture, Strings.PluginDisabledInConfig, nameof(SteamTokenDumperPlugin)));
 
@@ -132,6 +130,8 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 			}
 		}
 
+		Config = config;
+
 #pragma warning disable CA5394 // This call isn't used in a security-sensitive manner
 		TimeSpan startIn = TimeSpan.FromMinutes(Random.Shared.Next(SharedInfo.MinimumMinutesBeforeFirstUpload, SharedInfo.MaximumMinutesBeforeFirstUpload));
 #pragma warning restore CA5394 // This call isn't used in a security-sensitive manner
@@ -144,7 +144,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		ASF.ArchiLogger.LogGenericInfo(string.Format(CultureInfo.CurrentCulture, Strings.PluginInitializedAndEnabled, nameof(SteamTokenDumperPlugin), startIn.ToHumanReadable()));
 	}
 
-	public async void OnBotDestroy(Bot bot) {
+	public async Task OnBotDestroy(Bot bot) {
 		if (bot == null) {
 			throw new ArgumentNullException(nameof(bot));
 		}
@@ -160,7 +160,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 	}
 
-	public async void OnBotInit(Bot bot) {
+	public async Task OnBotInit(Bot bot) {
 		if (bot == null) {
 			throw new ArgumentNullException(nameof(bot));
 		}
@@ -179,7 +179,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 	}
 
-	public void OnBotSteamCallbacksInit(Bot bot, CallbackManager callbackManager) {
+	public Task OnBotSteamCallbacksInit(Bot bot, CallbackManager callbackManager) {
 		if (bot == null) {
 			throw new ArgumentNullException(nameof(bot));
 		}
@@ -193,7 +193,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 
 		if (Config is not { Enabled: true }) {
-			return;
+			return Task.CompletedTask;
 		}
 
 		subscription = callbackManager.Subscribe<SteamApps.LicenseListCallback>(callback => OnLicenseList(bot, callback));
@@ -201,13 +201,19 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		if (!BotSubscriptions.TryAdd(bot, subscription)) {
 			subscription.Dispose();
 		}
+
+		return Task.CompletedTask;
 	}
 
-	public IReadOnlyCollection<ClientMsgHandler>? OnBotSteamHandlersInit(Bot bot) => null;
+	public Task<IReadOnlyCollection<ClientMsgHandler>?> OnBotSteamHandlersInit(Bot bot) => Task.FromResult((IReadOnlyCollection<ClientMsgHandler>?) null);
 
-	public override void OnLoaded() => Utilities.WarnAboutIncompleteTranslation(Strings.ResourceManager);
+	public override Task OnLoaded() {
+		Utilities.WarnAboutIncompleteTranslation(Strings.ResourceManager);
 
-	public void OnPICSChanges(uint currentChangeNumber, IReadOnlyDictionary<uint, SteamApps.PICSChangesCallback.PICSChangeData> appChanges, IReadOnlyDictionary<uint, SteamApps.PICSChangesCallback.PICSChangeData> packageChanges) {
+		return Task.CompletedTask;
+	}
+
+	public Task OnPICSChanges(uint currentChangeNumber, IReadOnlyDictionary<uint, SteamApps.PICSChangesCallback.PICSChangeData> appChanges, IReadOnlyDictionary<uint, SteamApps.PICSChangesCallback.PICSChangeData> packageChanges) {
 		if (currentChangeNumber == 0) {
 			throw new ArgumentOutOfRangeException(nameof(currentChangeNumber));
 		}
@@ -221,7 +227,7 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 
 		if (Config is not { Enabled: true }) {
-			return;
+			return Task.CompletedTask;
 		}
 
 		if (GlobalCache == null) {
@@ -229,15 +235,17 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 
 		GlobalCache.OnPICSChanges(currentChangeNumber, appChanges);
+
+		return Task.CompletedTask;
 	}
 
-	public void OnPICSChangesRestart(uint currentChangeNumber) {
+	public Task OnPICSChangesRestart(uint currentChangeNumber) {
 		if (currentChangeNumber == 0) {
 			throw new ArgumentOutOfRangeException(nameof(currentChangeNumber));
 		}
 
 		if (Config is not { Enabled: true }) {
-			return;
+			return Task.CompletedTask;
 		}
 
 		if (GlobalCache == null) {
@@ -245,6 +253,8 @@ internal sealed class SteamTokenDumperPlugin : OfficialPlugin, IASF, IBot, IBotS
 		}
 
 		GlobalCache.OnPICSChangesRestart(currentChangeNumber);
+
+		return Task.CompletedTask;
 	}
 
 	private static async void OnBotRefreshTimer(object? state) {