fix(whoami): convert retrieval scores to float

[INo-xious]

Purpose

Fix WhoAmI documentation retrieval failing when FAISS returns NumPy floating-point scores that the generated ROS response rejects.

Proposed Changes

• Convert each score with float() at the ROS response boundary, preserving values and document ordering.
• Add regression coverage using the real callback and generated VectorStoreRetrieval.Response for NumPy float32 scores, Python floats, and empty results. Explicitly enable field validation on generators where it is optional.

Issues

Addresses the score serialization failure in #565.

Testing

• ROS Jazzy, Python 3.12, with rai_interfaces built from source.
• python -m pytest tests/rai_whoami/test_vector_store_retrieval_agent.py --timeout=60: before the fix, 1 failed with the reported score assertion and 2 passed; after the fix, all 3 passed.
• Live ROS service round trips with the real connector and mocked retrieval: all 3 cases passed with field validation enabled.
• pre-commit run --all-files: all 13 hooks passed, including Ruff and formatting.
• uv lock --check and git diff --check passed.
• Humble and the full repository suite were not run.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.61%. Comparing base (6802d40) to head (a57f20b).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #876   +/-   ##
=======================================
  Coverage   74.61%   74.61%           
=======================================
  Files          83       83           
  Lines        3652     3652           
=======================================
  Hits         2725     2725           
  Misses        927      927           

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