fix: bootstrap custom pull event handler from local repo

[isc-pbarton]

Description

Resolves #1000
When changes are imported through a pull event handler and there's a custom pull event handler that has needs to be loaded/compiled, we now import it from the local repository / compile it. This fix makes it smoother to onboard a new instance with Import All. A side effect is that changes to a custom pull event handler will now be reflected immediately on pull.

Assumption: a custom pull event handler has no other dependencies in the repo. I think we shouldn't bother with any special handling around that case unless somebody requests it.

Testing

Unit test fully covers expected behavior (thanks Claude)

Checklist

• This branch has the latest changes from the main branch rebased or merged.
• [N/A] Web UI has been built (any changes in git-webui/src have matching changes in git-webui/release)
• CHANGELOG.md entry added if appropriate.
• [N/A] Documentation has been/will be updated

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 50.47%. Comparing base (14ca955) to head (b701a9d).

Files with missing lines	Patch %	Lines
cls/SourceControl/Git/PullEventHandler.cls	95.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1005      +/-   ##
==========================================
+ Coverage   49.95%   50.47%   +0.51%     
==========================================
  Files          23       23              
  Lines        3375     3394      +19     
==========================================
+ Hits         1686     1713      +27     
+ Misses       1689     1681       -8     

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