feat(cli): `manim-slides checkhealth`

[jeertmans]

Closes #457

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.36%. Comparing base (8c0dd6a) to head (3b7e78a).

Files	Patch %	Lines
manim_slides/checkhealth.py	71.42%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #458      +/-   ##
==========================================
- Coverage   80.37%   80.36%   -0.02%     
==========================================
  Files          22       23       +1     
  Lines        1824     1833       +9     
==========================================
+ Hits         1466     1473       +7     
- Misses        358      360       +2     

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