test: add unit tests for minio infra and upload_requests service

[ademboukabes]

Description

This PR introduces comprehensive unit tests for two critical backend components (Phases 3 and 4 of our testing roadmap).

Key Additions:

1. MinIO Infrastructure (app/infra/minio.py)

• Added mock tests for all bucket operations (put, get, delete, copy).
• Covered S3Error exception handling.
• Implemented file extension validation tests for image buckets.

2. Upload Requests Service (app/service/upload_requests.py)

• Thoroughly mocked all external dependencies (GoogleDriveClient, NatsClient, StagedUploadStorageService) and DB queriers.
• Tested single photo uploads, folder batch processing, and approval workflows.
• Validated rollback mechanisms and SQL integrity error handling (Conflict scenarios).

Verification:

• Full CI test suite has been executed locally.
• All tests (184/184) passed successfully.
• Linter (ruff) rules respected.