feat: footnote specs and ordering options

[rich-iannone]

This PR adds to the footnote system in the library and focuses on customization and flexibility in footnote rendering. We now include options and methods for controlling footnote mark formatting and ordering. Part of this is also some improvements to the HTML rendering logic for footnotes (along with expanded support for styling footnotes via location selectors). The updates in this PR will provide users with more fine-grained control over how footnotes appear and are ordered in tables.

[codecov]

Codecov Report

❌ Patch coverage is 97.14286% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.66%. Comparing base (e419e98) to head (94462d8).

Files with missing lines	Patch %	Lines
great_tables/_utils_render_html.py	96.52%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #884      +/-   ##
==========================================
- Coverage   98.69%   98.66%   -0.04%     
==========================================
  Files          51       51              
  Lines        7824     7924     +100     
==========================================
+ Hits         7722     7818      +96     
- Misses        102      106       +4     

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