test(qdrant): add unit tests for target connector helpers

[nuthalapativarun]

Summary

• Add unit tests for the Qdrant target connector helper functions
• Tests cover _distance_from_spec, _multivector_comparator, and _vector_params_from_def
• All tests run without a live Qdrant service; the full test class is skipped when qdrant-client is not installed (mirrors the pattern used in test_turbopuffer_target.py)

The Qdrant connector was the only vector connector without any test coverage.

Test plan

• uv run pytest python/tests/connectors/test_qdrant_target.py -v
• uv run ruff format --check .
• uv run ruff check .

[nuthalapativarun]

Hi, just checking in on this PR — let me know if you need any changes or have any feedback. Happy to update if needed!