Add AI avatar disclosure session option

[bc-anam]

Summary

• add optional SessionOptions.show_ai_avatar_disclosure
• serialize it as showAiAvatarDisclosure only when explicitly set
• preserve positional compatibility for the existing egress argument
• document that the enabled disclosure remains visible throughout the session

Test plan

• uv run pytest -q: 60 passed on the full branch suite; focused client suite passes
• Ruff format and lint pass

Repository-wide mypy currently reports existing errors in signalling and streaming modules unrelated to this change.

Related

• Lab policy/API: https://github.com/anam-org/anam-lab/pull/1874
• Engine: https://github.com/anam-org/anam-engine/pull/3176

[cubic-dev-ai]

All reported issues were addressed across 3 files

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[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

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[sr-anam]

Updated note: Lab/direct API routes still support showAIAvatarDisclosure on /engine/session, and the Python SDK starts sessions through that direct API-key path. This SDK update is therefore still needed for Python users to request Anam-rendered disclosure on direct /engine/session sessions. The session-token path can continue to set the same disclosure behavior separately.

[sr-anam]

Turns out the python sessions dont call session-token so we need to support it in the sdk