Add simple polars explorer

[hoxbro]

Fixes #1339

However, I get TypeErrors when moving around the UI. Need to look into if it is directly related to the conversion.

[codecov]

Codecov Report

Attention: Patch coverage is 20.00000% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 87.31%. Comparing base (6c96c7e) to head (23d9f0c).

Files	Patch %	Lines
hvplot/plotting/core.py	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1340      +/-   ##
==========================================
- Coverage   87.39%   87.31%   -0.08%     
==========================================
  Files          50       50              
  Lines        7490     7499       +9     
==========================================
+ Hits         6546     6548       +2     
- Misses        944      951       +7     

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[hoxbro]

Suggested change

	ys for ys in (self._data[y] for y in y) if len(ys) and ys.dtype.kind not in 'OSU'
	ys for ys in (self._data[y] for y in y) if len(ys) and (hasattr(ys, 'dtype') and ys.dtype.kind not in 'OSU')