refactor: separate Nakama provider concerns into context, refs, and state modules

- Extracted context contract to `contexts.ts` (NakamaContextType)
- Added strongly typed internal provider refs in `refs.ts`
  - socketRef: React.RefObject<Socket | null>
  - gameMetadataRef: React.RefObject<GameMetadata | null>
- Added `NakamaProviderState` in `states.ts` for React-managed provider state
  - session, socket, matchId, matchmakerTicket
- Refactored NakamaProvider to use new modular structure
  - Replaced scattered useState/useRef with structured internal state + refs
  - Updated onMatchData to use MatchDataMessage model
  - Replaced deprecated MutableRefObject typing with RefObject
  - Cleaned update patterns using `updateState` helper
- Updated imports to use new models and context structure
- Improved separation of responsibilities:
  - models = pure domain types
  - context = exposed provider API
  - refs = internal mutable runtime refs
  - state = provider-managed reactive state
- Ensured all Nakama provider functions fully typed and consistent with TS

This refactor improves clarity, type safety, and maintainability for the
Nakama real-time multiplayer provider.

src/interfaces/models.ts

@@ -0,0 +1,36 @@
+export interface PlayerModel {
+  user_id: string;
+  username: string;
+  index: number;
+  metadata: Record<string, string>; // e.g. { symbol: "X" }
+}
+
+export interface MatchDataMessage<T = any> {
+  opCode: number;
+  data: T;
+  userId: string | null;
+}
+
+export interface Board {
+  grid: string[][];
+}
+
+export interface GameState {
+  boards: Record<string, Board>;
+  turn: number;
+  winner: string | null;
+  gameOver: boolean;
+  players: PlayerModel[];
+  metadata: Record<string, any>;
+}
+
+export interface GameMetadata {
+  game: string;
+  mode: string;
+}
+
+export interface MatchDataMessage<T = any> {
+  opCode: number;
+  data: T;
+  userId: string | null;
+}