chore: Add POLARS_TIMEOUT_MS for timing out slow Polars tests

[orlp]

This adds the environment variable POLARS_TIMEOUT_MS that when set will cause any call to any Polars function automatically exit the process with an error if the function still isn't finished after that many milliseconds has passed. This is useful for figuring out with pytest which test is hanging, if any.

I've also turned it on in the CI and Makefile when testing, defaulting to 60 seconds. This may need to be raised, we'll see.

If the environment variable POLARS_TIMEOUT_MS is not set when the first call to a Polars function is made, the mechanic is disabled entirely for performance.

[codecov]

Codecov Report

Attention: Patch coverage is 90.16393% with 6 lines in your changes missing coverage. Please review.

Project coverage is 80.92%. Comparing base (4fd8d57) to head (923198e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-python/src/timeout.rs	89.83%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21887      +/-   ##
==========================================
- Coverage   80.93%   80.92%   -0.01%     
==========================================
  Files        1624     1625       +1     
  Lines      234643   234704      +61     
  Branches     2693     2693              
==========================================
+ Hits       189899   189929      +30     
- Misses      44110    44141      +31     
  Partials      634      634              

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