feat: list & array measures of dispersion

[ion-elgreco]

Summary:

• Adds measures to arr and list namespace on Expr and Series
• Adds support for pl.Duration inner dtypes (for var, cast first to ms to prevent overflow)
• Adds tests

@stinodego I saw that there we some fast paths for other methods like sum where if the series doesn't contain nulls the values are collected from a slice and then summed. Should I do something similar for std, var and median here?

• closes: Add statistical methods to the List namespace (median, std, var) #9033

[ion-elgreco]

@reswqa could you perhaps review this PR?

[reswqa]

Thanks for the contribution. This change overall looks good. I left a few comments. Also cc @ritchie46 for reviewing.

[ion-elgreco]

Is there something else required to get this merged? :)

[reswqa]

Is there something else required to get this merged? :)

No, but we need to wait for Ritchie to make the final review.

[ion-elgreco]

@reswqa ah okay!

[ritchie46]

Thank you @ion-elgreco. Can you rebase? Then we can merge.

[ion-elgreco]

@ritchie46 Done : )