Format Polars objects using Polars' internal x._s.get fmt() method

[mwouts]

Closes #471

TODO:

• Remove the additional string added to the "enum" types
• Get a proper formatting for pl.DataFrame({"float": [math.pi, math.pi * 1e12]}) (get 3.1416e12 for the second row, not 3141600000000 as currently)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 96.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.85%. Comparing base (3dc4eb4) to head (824ef99).

Files with missing lines	Patch %	Lines
src/itables/datatables_format.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #474      +/-   ##
==========================================
+ Coverage   93.83%   93.85%   +0.02%     
==========================================
  Files          46       46              
  Lines        2367     2409      +42     
==========================================
+ Hits         2221     2261      +40     
- Misses        146      148       +2     

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[github-actions]

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[mwouts]

There is currently no public function that one can use instead of ._s.get_fmt, cf. pola-rs/polars#25880. I'll give another try at the str conversion for complex types, and possibly use ._s.get_fmt with a safety fallback if it was bound to change.