Modernize lock object declarations from object to System.Threading.Lock

Replace all lock object declarations using 'object' type with the C# 13
System.Threading.Lock type across 12 files. The Lock type provides a
more efficient locking mechanism - when used with lock(), the compiler
automatically uses Lock.EnterScope() instead of Monitor.Enter/Exit.

Also made two previously non-readonly lock fields readonly:
- McClient.DigLock
- Protocol18.MessageSigningLock

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

MinecraftClient/Scripting/ChatBot.cs

@@ -4,6 +4,7 @@ using System.IO;
 using System.Linq;
 using System.Text;
 using System.Text.RegularExpressions;
+using System.Threading;
 using Brigadier.NET;
 using MinecraftClient.CommandHandler;
 using MinecraftClient.Inventory;
@@ -42,7 +43,7 @@ namespace MinecraftClient.Scripting
         private McClient? _handler = null;
         private ChatBot? master = null;
         private readonly List<string> registeredPluginChannels = new();
-        private readonly object delayTasksLock = new();
+        private readonly Lock delayTasksLock = new();
         private readonly List<TaskWithDelay> delayedTasks = new();
         protected McClient Handler
         {