perf: Improve rolling_median algorithm

[ritchie46]

This removes quadratic worst case to O(nlogk).

closes #12609

0.19.x

polars,median,single,1000000,100,0.085
polars,median,single,1000000,1000,0.161
polars,median,single,1000000,10000,0.798
polars,median,single,10000000,100,0.849
polars,median,single,10000000,1000,1.663
polars,median,single,10000000,10000,8.597
polars,median,single,100000000,100,9.060
polars,median,single,100000000,1000,17.968
polars,median,single,100000000,10000,94.659

PR

polars,median,single,1000000,100,0.080
polars,median,single,1000000,1000,0.094
polars,median,single,1000000,10000,0.111
polars,median,single,10000000,100,0.777
polars,median,single,10000000,1000,0.943
polars,median,single,10000000,10000,1.120
polars,median,single,100000000,100,7.969
polars,median,single,100000000,1000,9.795
polars,median,single,100000000,10000,11.813

[jangorecki]

is documentation coming in this PR later on or it will some different PR? reading rust is not yet that fluent for me. I am interested about implementation used precisely.