Split extension methods into separate classes (#161)

This PR splits the extension methods contained in `Extensions.cs` into
separate classes in the `Octobot.Extensions` namespace. This was done
for multiple reasons:
1) The `Extensions.cs` violates SRP (Single Responsibility Principle) -
it takes upon itself every extension method for many types
2) Having a separate class for each extended type is a standard practice
- take a look at
[Remora.Discord](https://github.com/Remora/Remora.Discord/tree/main/Backend/Remora.Discord.Rest/Extensions)
or [osu!](https://github.com/ppy/osu/tree/master/osu.Game/Extensions)
3) Having all extension methods in one file makes it hard to find the
method you want

src/Extensions/LoggerExtensions.cs

@@ -0,0 +1,35 @@
+using Microsoft.Extensions.Logging;
+using Remora.Discord.Commands.Extensions;
+using Remora.Results;
+
+namespace Octobot.Extensions;
+
+public static class LoggerExtensions
+{
+    /// <summary>
+    ///     Checks if the <paramref name="result" /> has failed due to an error that has resulted from neither invalid user
+    ///     input nor the execution environment and logs the error using the provided <paramref name="logger" />.
+    /// </summary>
+    /// <remarks>
+    ///     This has special behavior for <see cref="ExceptionError" /> - its exception will be passed to the
+    ///     <paramref name="logger" />
+    /// </remarks>
+    /// <param name="logger">The logger to use.</param>
+    /// <param name="result">The Result whose error check.</param>
+    /// <param name="message">The message to use if this result has failed.</param>
+    public static void LogResult(this ILogger logger, IResult result, string? message = "")
+    {
+        if (result.IsSuccess || result.Error.IsUserOrEnvironmentError())
+        {
+            return;
+        }
+
+        if (result.Error is ExceptionError exe)
+        {
+            logger.LogError(exe.Exception, "{ErrorMessage}", message);
+            return;
+        }
+
+        logger.LogWarning("{UserMessage}\n{ResultErrorMessage}", message, result.Error.Message);
+    }
+}