feat(matchmaking): replace legacy rpc_find_match with Nakama native matchmaking

### Summary
This update removes the old RPC-driven matchmaking flow and replaces it
with proper Nakama matchmaker integration. Players now queue using
`matchmaker_add` over WebSockets, and matches are created via
`MatchmakerMatched` callback.

### Changes
- Removed `rpc_find_match` and MatchList polling logic
- Added `MatchmakerMatched` handler to auto-create TicTacToe matches
- Added RPC stubs `join_matchmaking` & `leave_matchmaking` only for
  optional validation (no server-side queueing)
- Updated `main.go` to register:
  ✅ `tictactoe` authoritative match
  ✅ `matchmaker_matched` callback
  ✅ removed obsolete rpc_find_match registration
- Ensured module loads successfully with cleaner InitModule
- Cleaned unused imports and outdated Nakama calls

### Benefits
- Fully scalable & production-ready matchmaking flow
- Eliminates race conditions & manual match assignment
- Supports multiple queues (classic / blitz) via string properties
- Aligns plugin with Nakama best practices
- Enables Python/WebSocket simulation without RPC dependencies

plugins/main.go

@@ -7,12 +7,13 @@ import (
 	"github.com/heroiclabs/nakama-common/runtime"
 )
 
+// Example RPC
 func HelloWorld(
-  ctx context.Context,
-  logger runtime.Logger,
-  db *sql.DB,
-  nk runtime.NakamaModule,
-  payload string,
+	ctx context.Context,
+	logger runtime.Logger,
+	db *sql.DB,
+	nk runtime.NakamaModule,
+	payload string,
 ) (string, error) {
 	logger.Info("HelloWorld RPC called — payload: %s", payload)
 	return `{"message": "Hello from Go RPC!"}`, nil
@@ -34,8 +35,13 @@ func InitModule(
 		logger.Error("Failed to register RPC: %v", err)
 		return err
 	}
-	if err := initializer.RegisterRpc("rpc_find_match", rpcFindMatch); err != nil {
-		logger.Error("RegisterRpc rpc_find_match failed: %v", err)
+  // Match making
+	if err := initializer.RegisterRpc("leave_matchmaking", rpcLeaveMatchmaking); err != nil {
+		logger.Error("RegisterRpc leave_matchmaking failed: %v", err)
+		return err
+	}
+	if err := initializer.RegisterMatchmakerMatched(MatchmakerMatched); err != nil {
+		logger.Error("RegisterMatchmakerMatched failed: %v", err)
 		return err
 	}