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/config/sample-script-packet-capture.cs

@@ -4,12 +4,14 @@ MCC.LoadBot(new PacketCadenceCaptureBot());
 
 //MCCScript Extensions
 
+using System.Threading;
+
 public class PacketCadenceCaptureBot : ChatBot
 {
     private const int CaptureDurationSeconds = 5;
     private const int CaptureDurationTicks = CaptureDurationSeconds * 20;
 
-    private readonly object _countsLock = new();
+    private readonly Lock _countsLock = new();
     private readonly Dictionary<string, int> _counts = new()
     {
         { "PlayerMovement", 0 },