Use pytest markers to gate Rapid/HNS tests

[ankitaluthra1]

• This PR removes HNS and Rapid support experimemtal feature flag as primary gate for HNS/Rapid tests.
• This PR refactors the test suite by introducing standardized pytest markers (requires_real_gcs, requires_hns, and requires_rapid) to replace manual environment variable checks for bucket types.
• These markers are defined in conftest.py and registered in pyproject.toml.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.50%. Comparing base (dc691ef) to head (a6f308d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #848   +/-   ##
=======================================
  Coverage   88.50%   88.50%           
=======================================
  Files          15       15           
  Lines        2993     2993           
=======================================
  Hits         2649     2649           
  Misses        344      344           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.