improve rolling_var performance

[ritchie46]

This wraps the performance improvements of the rolling_window kernels.

All kernels now maintain a state and will do a lot less work than previously.

[codecov-commenter]

Codecov Report

Merging #3470 (a0bd43d) into master (69c57d4) will increase coverage by 0.04%.
The diff coverage is 91.02%.

@@            Coverage Diff             @@
##           master    #3470      +/-   ##
==========================================
+ Coverage   77.57%   77.62%   +0.04%     
==========================================
  Files         406      408       +2     
  Lines       69746    69847     +101     
==========================================
+ Hits        54108    54217     +109     
+ Misses      15638    15630       -8     

Impacted Files	Coverage Δ
polars/polars-arrow/src/kernels/rolling/mod.rs	94.80% <ø> (ø)
.../polars-arrow/src/kernels/rolling/no_nulls/mean.rs	50.94% <ø> (ø)
...ars/polars-arrow/src/kernels/rolling/nulls/mean.rs	98.00% <ø> (-0.04%)	⬇️
...lars/polars-arrow/src/kernels/rolling/nulls/sum.rs	92.72% <ø> (ø)
...olars-core/src/chunked_array/ops/rolling_window.rs	96.80% <ø> (ø)
...polars-arrow/src/kernels/rolling/nulls/variance.rs	86.02% <86.02%> (ø)
...ars-arrow/src/kernels/rolling/no_nulls/variance.rs	93.19% <93.19%> (ø)
...s/polars-arrow/src/kernels/rolling/no_nulls/mod.rs	93.33% <100.00%> (+5.06%)	⬆️
...lars/polars-arrow/src/kernels/rolling/nulls/mod.rs	100.00% <100.00%> (+19.91%)	⬆️
...olars-lazy/src/physical_plan/expressions/column.rs	63.63% <0.00%> (-10.61%)	⬇️
... and 14 more

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