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 82.36%. Comparing base (773936d) to head (4344a39).
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   82.35%   82.36%           
=======================================
  Files         338      338           
  Lines       50957    50975   +18     
=======================================
+ Hits        41966    41985   +19     
+ Misses       8991     8990    -1     

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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?