Add support for serializing polars DataFrame

[philippjfr]

Partial fix for #7468

We additionally need to allow param.DataFrame to accept non-pandas DataFrames, either by default or as an option.

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 8 lines in your changes missing coverage. Please review.

Project coverage is 86.72%. Comparing base (64e9992) to head (90a764c).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/io/datamodel.py	55.55%	8 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7475       +/-   ##
===========================================
+ Coverage   71.66%   86.72%   +15.06%     
===========================================
  Files         345      346        +1     
  Lines       52032    52051       +19     
===========================================
+ Hits        37287    45143     +7856     
+ Misses      14745     6908     -7837     

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[MarcSkovMadsen]

Partial fix for #7468

We additionally need to allow param.DataFrame to accept non-pandas DataFrames, either by default or as an option.

My vision for the DataFrame parameter is that there is a parameter that supports any kind of tabular data source including the ones supported by Narwhals. See narwhals-dev/narwhals#1289. This means broading the concept from DataFrame to Tabular or Columnar data source. Why can't I use a database as the remote backend for Tabulator? Or a .parquet file?

[philippjfr]

pre-commit.ci autofix

[philippjfr]

This change won't do anything yet but it makes sense to merge in anticipation to the coming changes in param.