feat: add the fmt_chem() function

[rich-iannone]

This PR adds the fmt_chem() method and the vals.fmt_chem() function. Both enable chemistry-aware formatting for both table columns and value lists.

[codecov]

Codecov Report

❌ Patch coverage is 81.95489% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.36%. Comparing base (8716b44) to head (456e6c5).

Files with missing lines	Patch %	Lines
great_tables/_formats.py	80.95%	24 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #887      +/-   ##
==========================================
- Coverage   98.64%   98.36%   -0.28%     
==========================================
  Files          52       52              
  Lines        8019     8152     +133     
==========================================
+ Hits         7910     8019     +109     
- Misses        109      133      +24     

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