feat: Allow for rolling_*_by to use index count as window

[MarcoGorelli]

example:

In [1]: import polars as pl
   ...: 
   ...: df = pl.DataFrame({"a": [1, 4, 2, 5]}).with_row_index()
   ...: print(df.with_columns(pl.col("a").rolling_sum_by("index", "2i")))
   ...: 
shape: (4, 2)
┌───────┬─────┐
│ index ┆ a   │
│ ---   ┆ --- │
│ u32   ┆ i64 │
╞═══════╪═════╡
│ 0     ┆ 1   │
│ 1     ┆ 5   │
│ 2     ┆ 6   │
│ 3     ┆ 7   │
└───────┴─────┘

which DataFrame.rolling already supports

It should be possible for both Expr.rolling_*_by and DataFrame.rolling to support Duration and Time too, but i'll keep that separate

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 79.77%. Comparing base (eb615e0) to head (a0ed213).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...s-time/src/chunkedarray/rolling_window/dispatch.rs	50.00%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19071   +/-   ##
=======================================
  Coverage   79.77%   79.77%           
=======================================
  Files        1531     1531           
  Lines      208500   208505    +5     
  Branches     2913     2913           
=======================================
+ Hits       166322   166326    +4     
- Misses      41627    41628    +1     
  Partials      551      551           

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[HansBambel]

Am I missing something or is the parameterized dtype never used?

Shouldn't it be something like this:

df = pl.DataFrame({"val": [1, 2, 3]}, schema={"val": dtype}).with_row_index()

[MarcoGorelli]

thanks @HansBambel , the intention was probably

df = pl.DataFrame({"val": [1, 2, 3]}).with_row_index().with_columns(pl.col('index').cast(dtype))

fancy making a pr to address this?

[HansBambel]

@MarcoGorelli I'll do that on the weekend at the latest!

[HansBambel]

Managed to do it now already: #19555

Local tests were failing because connectorx was missing even after running make requirements-all. Not sure why