Feat/faster session start

[sebvanleuven]

Introducing the API session start route to improve session start times, which avoids fetching a token first (RTT + TLS handshake) to start the session.

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Summary by cubic

Start sessions directly with the API key to remove the token prefetch step and cut one network round-trip, speeding up session start. Improves error handling, simplifies the client, and cleans up docstrings.

• Refactors
  • Removed get_session_token and token storage; start_session now calls POST /engine/session with Authorization: Bearer <api_key>, including clientLabel, personaConfig, sessionOptions, and clientMetadata.
  • Clearer errors: 401 → AuthenticationError, 403 → SessionError, 5xx → SessionError, other unexpected responses → AnamError with better message fallback.
  • Simplified docstrings and updated logs to note direct API-key auth.

^{Written for commit 50bfed2. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 1 file

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Fix all with cubic | Re-trigger cubic</sub>