fix(gemini): support file retrieval in GoogleAIStudioFilesHandle

[varunsripad123]

ixes #20007
This PR implements file_retrieve support in GoogleAIStudioFilesHandler. Previously, attempting to retrieve a file (e.g., to check status) would raise a NotImplementedError or return 500, making it impossible to check if a file was ACTIVE before use.

Changes

• Implemented transform_retrieve_file_request in litellm/llms/gemini/files/transformation.py to construct the correct Google AI Studio API URL (v1beta/files/{file_id}).
• Implemented transform_retrieve_file_response to map Gemini file states (ACTIVE, PROCESSING, FAILED) to standard OpenAI statuses (processed, uploaded, error).

Testing

• Verified manually with a reproduction script testing URL construction and status mapping.

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Project	Deployment	Actions	Updated (UTC)
litellm	Error		Jan 29, 2026 9:17pm

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[Sameerlite]

LGTM