fix: clean up cruft in source version fetching and include excludes

[beckermr]

Description:

This PR cleans up some cruft in source version fetching, adds a few type hints, and accounts for excludes when fetching versions.

Checklist:

• Pydantic model updated or no update needed

Cross-refs, links to issues, etc:

[codecov]

Codecov Report

❌ Patch coverage is 70.29703% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.64%. Comparing base (84c74ba) to head (732cd02).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
conda_forge_tick/update_sources.py	68.08%	30 Missing ⚠️

❌ Your patch status has failed because the patch coverage (70.29%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4829      +/-   ##
==========================================
- Coverage   80.70%   80.64%   -0.07%     
==========================================
  Files         143      143              
  Lines       16459    16485      +26     
==========================================
+ Hits        13284    13295      +11     
- Misses       3175     3190      +15     

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