fix: Enhance EFV audit logs

[SahilJat]

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Changes

Closes #7526

This PR resolves the issue of opaque audit logs for v2 versioning (EnvironmentFeatureVersion). Previously, publishing a new version only logged a static string ("New version published for feature: %s"), completely omitting which feature states were actually changed.

This updates create_environment_feature_version_published_audit_log_task to:

• Render the EFV message via get_updated_feature_states_for_version(efv).
• Enumerate each changed Feature State's action (enabled/disabled) and scope (Environment default, Segment override, Identity override).
• Mitigate N+1 database queries by prefetching feature_segment__segment and identity via select_related.

How did you test this code?

-I wrote comprehensive unit tests in api/tests/unit/audit/test_unit_audit_services.py to cover the different scenarios for the audit log task:

• Verified that if there are no changes, the audit log falls back to the original header-only format.
• Verified that modifications to the Environment Default are properly appended to the log string.
• Verified that modifications to a Segment Override append the specific Segment's name to the log string.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.31%. Comparing base (82c5dfb) to head (3eb06b6).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7535      +/-   ##
==========================================
- Coverage   98.47%   98.31%   -0.16%     
==========================================
  Files        1400     1400              
  Lines       53036    52960      -76     
==========================================
- Hits        52226    52068     -158     
- Misses        810      892      +82     

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[SahilJat]

@khvn26 the test cases that is failing is already existing issue which will be solved with pr #7530 . This issue is also solved please have a look at it. Thanks