Rename fns choose_multiple* → sample*; add choose*_iter

[dhardy]

• Added a CHANGELOG.md entry

Fixes #1620 by:

• Renaming IndexedRandom::choose_multiple* → sample*
• Renaming IteratorRandom::choose_multiple* → sample*
• Adding IndexedRandom::choose_iter, choose_weighted_iter

I think I'm happy to go with this. @vks, @benjamin-lieser review please.

[dhardy]

Note: I don't think we should add choose_mut_iter. Even if we wanted to, we couldn't do so using the Iterator trait; we'd need a streaming/borrowing iterator trait. The choose_iter fn here returns the same lifetime (that of the iterator) for each next sample.

I briefly considered deprecating all the choose_mut fns but a GitHub search shows some uses.

[dhardy]

This uses RPIT, stabilised in Rust 1.75. We will need to update the MSRV to 1.85 anyway for chacha20, so I'll make a new PR for that...