feat(mr-search): Target specific project from MR URL instead of searching all projects

[M0nkeySan]

Why

When searching for a merge request using its URL, we were unnecessarily querying all accessible projects,
even though the URL already contains the exact project path. This led to:

• Multiple unnecessary API calls (one per project)
• Potential timeouts on the Slack command due to high latency
• Wasted GitLab API rate limiting quota

Improvements

• Extract the project path directly from the merge request URL
• Make a single API call to the specific project
• Eliminate the need to iterate through all projects

Example:
For URL: https://gitlab.com/group/project/-/merge_requests/123

• Before: Query MR #123 in every accessible project (~N API calls)
• After: Query MR #123 only in 'group/project' (1 API call)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.35%. Comparing base (678107d) to head (09c5d36).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #48      +/-   ##
==========================================
+ Coverage   78.26%   78.35%   +0.09%     
==========================================
  Files          94       94              
  Lines        1909     1917       +8     
  Branches      345      341       -4     
==========================================
+ Hits         1494     1502       +8     
- Misses        387      406      +19     
+ Partials       28        9      -19     

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