enh: Support polars in `pn.cache`

[hoxbro]

Resolves https://github.com/holoviz/panel/issues/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"])

[codecov[bot]]

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 :warning:

Additional details and impacted files

```diff @@ 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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