feat(python/fmt): create python writer interfaces

[jnooree]

Checklist

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Linked Issues

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• Closes Python molecule writer interface #283.

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[codecov]

Codecov Report

Attention: Patch coverage is 96.96970% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 90.79%. Comparing base (dea7728) to head (1f42945).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #285      +/-   ##
==========================================
+ Coverage   90.67%   90.79%   +0.11%     
==========================================
  Files          37       37              
  Lines        8636     8669      +33     
==========================================
+ Hits         7831     7871      +40     
+ Misses        805      798       -7     

Files	Coverage Δ
python/include/nuri/python/utils.h	94.53% <ø> (ø)
python/src/nuri/fmt/fmt_module.cpp	93.18% <96.96%> (+2.27%)	⬆️

... and 2 files with indirect coverage changes