feat: implement realtime client with WebSocket support

[Subbi8]

What kind of change does this PR introduce?

Feature - Adding a new realtime client implementation with WebSocket support for real-time data synchronization.

What is the current behavior?

Currently, the Supabase Python client lacks realtime functionality implementation. The test file test_realtime.py shows a NotImplementedError for realtime channel functionality, indicating this feature is missing.

What is the new behavior?

• Implemented a complete realtime client with WebSocket support
• Added three main classes:
  • RealtimeMessage: Handles message formatting and serialization
  • RealtimeChannel: Manages channel subscriptions and message routing
  • RealtimeClient: Manages WebSocket connections and heartbeat mechanism
• Added comprehensive test coverage with all tests passing
• Implemented proper thread management and cleanup
• Added support for channel subscriptions and message handling

Additional context

• The implementation follows the Phoenix WebSocket protocol used by Supabase
• Includes proper error handling and resource cleanup
• Added detailed documentation in NEW_CONTRIBUTION.md
• All tests are passing successfully, including integration tests
• The implementation is thread-safe and handles connection lifecycle properly

[silentworks]

This would not be a part of this repo. If you wish to contribute to the sync client for realtime, it should be done in the https://github.com/supabase/realtime-py repo.