feat: add registration dictionary and Register method

CommandHook/CommandHookModSystem.cs

@@ -1,14 +1,27 @@
-using Vintagestory.API.Server;
+using System.Collections.Generic;
 using Vintagestory.API.Common;
+using Vintagestory.API.Server;
 
 namespace CommandHook;
 
 public class CommandHookModSystem : ModSystem
 {
+    private readonly Dictionary<string, List<CommandRegistration>> _registrations = new();
+
     public override bool ShouldLoad(EnumAppSide forSide) => forSide == EnumAppSide.Server;
 
     public override void StartServerSide(ICoreServerAPI api)
     {
         Mod.Logger.Notification("[CommandHook] Loaded");
     }
+
+    public void Register(string modId, CommandRegistration registration)
+    {
+        if (!_registrations.TryGetValue(modId, out var list))
+        {
+            list = new List<CommandRegistration>();
+            _registrations[modId] = list;
+        }
+        list.Add(registration);
+    }
 }