fix(models): retry transient Gemini errors (504/503/500) and extend request timeout

[AdvancedUno]

Summary

Fixes the Gemini provider aborting resume extraction on transient 504 Deadline expired errors.

Two changes in GeminiProvider.chat() (models.py):

1. Extend the per-request deadline. Pass request_options={"timeout": 600} to generate_content(). The SDK's default per-request gRPC deadline (~60s) is too short for larger section calls on gemini-2.5-flash / gemini-3.5-flash, which raised DeadlineExceeded (504).
2. Retry transient server errors. The backoff loop previously only handled ResourceExhausted (429). It now also retries DeadlineExceeded (504), ServiceUnavailable (503), and InternalServerError (500) using the same exponential-backoff-with-jitter logic.

Previously, a single transient 504 on any section caused _extract_all_sections_separately to abort the whole run with no output.

Before / After

Before — one transient 504 aborts the entire extraction:

 Error calling LLM for projects section: 504 Deadline expired before operation could complete.
 Failed to extract projects section. Aborting extraction to prevent partial/invalid resume data.

After — transient errors are retried with backoff and the run completes:

[GeminiProvider] Transient error DeadlineExceeded (attempt 1/5). Retrying in 11.6s...
Total time for separate section extraction: 23.06 seconds
OVERALL SCORE: 75.0/100

Testing

• Ran python score.py <resume>.pdf end to end with LLM_PROVIDER=gemini, DEFAULT_MODEL=gemini-2.5-flash.
• Before: extraction aborted with 504 Deadline expired before operation could complete. on the projects / awards sections (reproduced across multiple runs).
• After: all six sections extract successfully, GitHub enrichment and evaluation complete, and a full report is produced.

Notes

• No prompt changes; provider-agnostic behavior preserved.
• Matched the surrounding code style (existing 2 ** attempt idiom, same retry-loop structure) rather than reformatting unrelated lines, to keep the diff focused on the fix.

Fixes #284