enh: Support polars in pn.cache

[hoxbro]

Resolves #7467

I need to add a test.

import polars as pl
from panel.io.cache import _polars_hash

df = pl.DataFrame({"column1": [1, 2, 3], "column2": ["a", "b", "c"]})

_polars_hash(df), _polars_hash(df.lazy()), _polars_hash(df["column1"])

[philippjfr]

Looks good, tests would be great.

[codecov]

Codecov Report

Attention: Patch coverage is 93.22034% with 4 lines in your changes missing coverage. Please review.

Project coverage is 82.32%. Comparing base (c06f779) to head (9cbf808).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
panel/io/cache.py	90.24%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7472      +/-   ##
==========================================
+ Coverage   82.30%   82.32%   +0.02%     
==========================================
  Files         338      338              
  Lines       50819    50889      +70     
==========================================
+ Hits        41825    41896      +71     
+ Misses       8994     8993       -1     

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