feat: add Register with frozen dictionary rebuild

CommandHook/CommandHookModSystem.cs

@@ -1,4 +1,5 @@
 using System.Collections.Frozen;
+using System.Collections.Generic;
 using HarmonyLib;
 using Vintagestory.API.Common;
 using Vintagestory.API.Server;
@@ -30,6 +31,31 @@ public class CommandHookModSystem : ModSystem
         Instance = null;
     }
 
+    public void Register(string modId, string commandName, CommandRegistration registration)
+    {
+        var builder = new Dictionary<string, Dictionary<string, CommandRegistration>>();
+
+        foreach (var (cmd, mods) in registrations)
+        {
+            var inner = new Dictionary<string, CommandRegistration>();
+            foreach (var (id, reg) in mods)
+                inner[id] = reg;
+            builder[cmd] = inner;
+        }
+
+        if (!builder.TryGetValue(commandName, out var target))
+        {
+            target = new Dictionary<string, CommandRegistration>();
+            builder[commandName] = target;
+        }
+        target[modId] = registration;
+
+        registrations = builder.ToFrozenDictionary(
+            pair => pair.Key,
+            pair => pair.Value.ToFrozenDictionary()
+        );
+    }
+
     public bool FireBefore(string commandName, ref CommandData data)
     {
         if (registrations.TryGetValue(commandName, out var mods))