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/refs.ts

@@ -0,0 +1,15 @@
+import React from "react";
+
+import {
+  Socket
+} from "@heroiclabs/nakama-js";
+
+import {
+  GameMetadata,
+} from './models'
+
+
+export interface NakamaRefs {
+  socketRef: React.RefObject<Socket | null>;
+  gameMetadataRef: React.RefObject<GameMetadata | null>;
+}