Chore Add session_ready callback

[sebvanleuven]

Add session_ready callback so consumer know when to start streaming.

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Summary by cubic

Adds a session_ready callback and SESSION_READY event so clients know exactly when the session is ready to receive TTS/user audio. Also improves connection close handling and cleanup for more reliable shutdowns.

• New Features

  • Added on_session_ready callback in streaming; client emits AnamEvent.SESSION_READY when the server signals SESSION_READY.

• Bug Fixes

  • Stronger close semantics: use ConnectionClosedCode, emit close once, distinguish server-closed vs WebRTC failures, and auto-close on server errors.
  • Better cleanup on close: clear message history, reset session state, guard against double close, and set closed before awaiting shutdown.
  • Faster/quieter connections: WebRTC timeout set to 2s; move ICE/data channel/close logs to debug.

^{Written for commit 1455bbc. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 4 files