[internal copy of #30137] perf(realtime): eliminate redundant per-frame JSON work on OpenAI realtime relay

[mateo-berri]

Automated copy of #30137 into litellm_internal_staging for pr-babysitter.

Original head: ma-armenta/litellm:litellm_realtime_beta_translation_latency @ a7d40f919870

[greptile-apps]

Greptile Summary

This PR eliminates redundant per-frame JSON work in the OpenAI Realtime relay. Previously each backend frame was deserialized up to three times (once in _handle_raw_backend_message, once in store_message, and once in _translate_event_to_beta); now the frame is parsed exactly once in the new _parse_backend_event static method and the resulting dict is threaded through all subsequent steps.

• store_message now accepts a pre-parsed dict, skips Pydantic construction entirely via an early _should_store_message check for events that won't be logged (e.g. audio deltas), and falls back to the raw dict on parse failure without re-checking the filter.
• _translate_event_to_beta returns the same event object (identity) when no translation applies, allowing the caller to forward raw_response without a json.dumps round-trip; a translated copy is only produced when at least one field changes.
• Eleven new tests cover the parse-once guarantee, the identity-return path, the skip-Pydantic fast path, and the GA/beta forwarding behavior end-to-end.

Confidence Score: 5/5

The change is safe to merge — it is a pure performance refactor of the raw backend message path with no changes to observable behavior for clients.

All three optimization paths (parse-once, skip-Pydantic, identity-return from _translate_event_to_beta) are mechanically correct and well-covered by the new test suite. The translated is event identity check is a valid Python idiom that is directly tested. The early _should_store_message gate preserves the existing behavior for tool-call collection (still called before the gate). No observable behavior changes for callers on either the GA or beta protocol paths.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/litellm_core_utils/realtime_streaming.py	Refactors the raw backend message path to parse each WebSocket frame's JSON exactly once, skips Pydantic construction for events that won't be logged, and returns the original event object from _translate_event_to_beta when no translation is needed so the caller can forward the raw frame without re-serializing.
tests/test_litellm/litellm_core_utils/test_realtime_streaming.py	Adds 11 new unit/async tests covering the parse-once guarantee, identity-return optimization, GA/beta client forwarding paths, drop behavior for conversation.item.done, and the skip-Pydantic fast path in store_message; also reformats a few existing multi-line assert messages.

_{Reviews (1): Last reviewed commit: "fix(realtime): widen store_message type ..." | Re-trigger Greptile}