Add copier-python CLI with update subcommand

[smkent]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 85.85366% with 29 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.12%. Comparing base (10aeb78) to head (39b115e).

Files with missing lines	Patch %	Lines
copier_python/repo.py	83.72%	11 Missing and 3 partials ⚠️
copier_python/__main__.py	86.11%	7 Missing and 3 partials ⚠️
copier_python/update.py	89.36%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              main      #64       +/-   ##
============================================
- Coverage   100.00%   86.12%   -13.88%     
============================================
  Files            1        4        +3     
  Lines            4      209      +205     
  Branches         0       19       +19     
============================================
+ Hits             4      180      +176     
- Misses           0       20       +20     
- Partials         0        9        +9     

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