Spike: Replace existing BranchesFinder with Gitlab::Git::Finders::RefsFinder

Summary

This is a spike to explore replacing the existing BranchesFinder with Gitlab::Git::Finders::RefsFinder to identify any missing functionality before proceeding with the full implementation.

Background

As part of the effort to move branch/tag searching to Gitaly (Epic &11057), we need to evaluate whether the new Gitlab::Git::Finders::RefsFinder can fully replace the existing BranchesFinder functionality.

The new RefsFinder was implemented in !125718 (merged) but is currently unused. This spike will help identify any gaps in functionality that need to be addressed.

Acceptance Criteria

Analyze the current BranchesFinder implementation and document all its features
Test Gitlab::Git::Finders::RefsFinder against the same use cases
Identify any missing functionality in the new finder
Document performance differences (if any)
Create follow-up issues for any identified gaps
Provide recommendation on whether to proceed with the replacement

Current Known Limitations

From the epic discussion, the new implementation currently has these limitations:

Only supports glob-based searching (no regular expression support)
No sorting support yet
No pagination support yet

Definition of Done

Comprehensive comparison document created
All missing functionality identified and documented
Follow-up issues created for any gaps
Clear recommendation provided on next steps