docs(python): Add missing Series methods to API reference

[henryharbeck]

Closes #17786

Missing doc items identified by looking at any methods without links here. Have validated that all works as expected against a local docs build.

Also note that Series does not implement many of the operator methods offered on DataFrame.

[MarcoGorelli]

would aggregation be a better section, as that's where it is for Expr?

[henryharbeck]

Thanks for the question and the quick review. Yes, I do think that's a better section - thanks for that.

It is in both aggregation and functions for Expr, so initially that was why I added it into computation. Upon reflection aggregation is indeed much better suited. Will update now.

[MarcoGorelli]

oh it's in both for Expr? 🤔 maybe the functions one can be removed then?

[MarcoGorelli]

Nice one, thanks @henryharbeck !

If you the wanted to de-dupe Expr.count (remove it from "functions"?) I think that'd be good too - is it the only one that's duplicated or are there others?

[MarcoGorelli]

If you the wanted to de-dupe Expr.count (remove it from "functions"?) I think that'd be good too - is it the only one that's duplicated or are there others?

edit: i asked about this, and devs are ok with some being in multiple places, so no need to change that for expr

[henryharbeck]

Thanks again @MarcoGorelli! 😃
Apologies to disappear after you replied to me 1 minute later 😅, was getting late and then had a busy weekend