DM-48159 : Make Coverage import optional

[tcjennings]

• Makes coverage import optional and lazy-loads it.
• Bump minimum Python to 3.11 (matching dependency for daf_butler).
• Add packaging extra option for coverage; i.e., pip users can specify pip install lsst-ctrl-mpexec[coverage]

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.03%. Comparing base (63cee0f) to head (7ed95cd).
Report is 4 commits behind head on main.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
tests/test_cliScript.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #316      +/-   ##
==========================================
+ Coverage   89.73%   90.03%   +0.30%     
==========================================
  Files          50       50              
  Lines        4520     4536      +16     
  Branches      414      414              
==========================================
+ Hits         4056     4084      +28     
+ Misses        340      327      -13     
- Partials      124      125       +1     

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[TallJimbo]

Looks great, thanks!