fix: return single_upload result from Project.upload()

[davidnichols-ops]

Summary

• Project.upload() was discarding the return value of single_upload(), always returning None even on successful uploads. This made it impossible for callers to inspect the upload response (image id, timing, retry counts) without calling single_upload() directly.
• Now returns the single_upload() result dict for single-file uploads (keys: image, annotation, upload_time, annotation_time, upload_retry_attempts, annotation_upload_retry_attempts).
• For directory uploads, returns a list of such dicts — one per successfully uploaded image. Skipped (non-image) files are excluded from the list.
• Existing callers that ignore the return value are completely unaffected — this is a backwards-compatible addition.

Closes #254.

Test plan

• python -m unittest passes — 731 tests, OK (skipped=1)
• New test test_upload_single_file_returns_result verifies single-file upload returns a dict with the expected image id
• New test test_upload_directory_returns_list_of_results verifies directory upload returns a list of dicts with correct count
• Updated existing test_project_methods in test_queries.py to assert the new return value (was asserting None)
• ruff check and ruff format --check pass on all modified files