Ref: Gemini multimodal live context window compression & session resumption #1974

[virendra-dhakhada]

Rebased version of [#1974], originally authored by @bo-socayo — all credit to them!

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Gemini Multimodal Live Context Window Compression & Session Resumption

This PR addresses the following problems:

1. ContextWindowCompressionConfig was not being set correctly on the Setup event. The context_window_compression field was missing on the model, so it wasn't being sent to the server—even if the client was configured to set it. Also, the type for sliding_window was incorrect (bool instead of dict), so it has been corrected to match the API specification: https://ai.google.dev/api/live#contextwindowcompressionconfig.

2. Added support for SessionResumptionConfig: https://ai.google.dev/api/live#sessionresumptionconfig.

3. Added support for handling the GoAway event: https://ai.google.dev/api/live#goaway.

   Currently, the SessionResumptionUpdate and GoAway events are simply logged. Implementing actual reconnection behavior is deferred to future work.

Example log message for the SessionResumptionUpdate event:

2025-06-07 04:27:20.357 | DEBUG | pipecat.services.gemini_multimodal_live.gemini:_handle_evt_session_resumption_update:944 - Gemini session resumption update: newHandle='CihvdGNnNThrcHM2eXZlenNiZzFyaTZqbmw4ZHk5dmh2ZnZ3aGRtaWRy' resumable=True lastConsumedClientMessageIndex=None

Partially addresses issue [#1606].