Update ServerContent and UsageMetadata live types

[tgodniak]

Summary

• Add candidates_token_count and candidates_tokens_details to Gemini.Types.Live.UsageMetadata — mirrors the fields already present in Gemini.Types.Response.UsageMetadata
• Add turn_complete_reason to Gemini.Types.Live.ServerContent — Vertex AI v1 field indicating why a turn completed (MALFORMED_FUNCTION_CALL, RESPONSE_REJECTED, NEED_MORE_INPUT)

Both fields are fully wired through @type t, defstruct, new/1, to_api/1, and from_api/1.

[nshkrdotcom]

Thanks @tgodniak. I used your PR as the guide for the final fix.

Your changes were the right starting point: they surfaced the missing Live API fields and helped pin down what Vertex Live v1 was sending. I ended up fixing the broader compatibility path around it as well, including Gemini Live vs Vertex Live usage field normalization, typed turn_complete_reason, downstream token accounting, and live-test behavior for environments that only expose native-audio Vertex Live models.

The full fix shipped in v0.11.1, and it's live on Hex here:
https://hex.pm/packages/gemini_ex/0.11.1

Appreciate you taking the time to put this together.