fix: update LiteLLM for security patches

[swolg]

Summary

• upgrade LiteLLM from 1.83.14 to 1.96.2
• address CVE-2026-49468 and other currently patchable LiteLLM advisories
• refresh UV and requirements locks, including compatible transitive dependencies
• bump flock-core to 0.5.601

Validation

• uv lock --check
• uv pip check
• pytest tests/test_transformers_provider.py tests/test_dspy_streaming_executor_helpers.py -q (31 passed)

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.01%. Comparing base (c13f1f0) to head (8e28aca).
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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #418   +/-   ##
=======================================
  Coverage   84.01%   84.01%           
=======================================
  Files         157      157           
  Lines       11160    11160           
  Branches     1536     1536           
=======================================
  Hits         9376     9376           
  Misses       1374     1374           
  Partials      410      410           

Flag	Coverage Δ
backend	84.01% <ø> (ø)

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