docs: Update by param description for rolling_*_by functions

[MarcoGorelli]

closes #19491

[rodrigogiraoserrao]

I'm assuming the types (U)Int32 / (U)Int64 are allowed because they can be interpreted as a timestamp (number of some-fraction-of-a-second since epoch), right?
Would it make sense to add a note regarding that?
Someone might be left thinking that (U)Ints of smaller precisions could still work and we just forgot to add them to the docstring..?

Dunno, just asking. Feel free to ignore 😬

[MarcoGorelli]

thanks for your review - they're allowed because you pass 'i' to mean "index count" to window_size, e.g. pl.col('price').rolling_mean_by('index', '3i')

[rodrigogiraoserrao]

Ah I see. Then the docstrings should probably say something about the i / index count, but that's maybe for another PR; i.e., not necessarily your responsibility here

[MarcoGorelli]

it's ok i can add it, thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.53%. Comparing base (1f104f9) to head (8a2e203).
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  Lines      217124   217124           
  Branches     2464     2464           
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+ Hits       172680   172694   +14     
+ Misses      43884    43870   -14     
  Partials      560      560           

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[rodrigogiraoserrao]

Thanks for making the docs clearer! 🚀