Rename repeatn

[SyxtonPrime]

As of rust 1.82.0, The standard library includes the function repeat_n (https://doc.rust-lang.org/std/iter/fn.repeat_n.html) which takes an element and a usize and constructs the iterator which repeats the element n times.

Rayon includes the same function (https://docs.rs/rayon/latest/rayon/iter/fn.repeatn.html) but uses a slightly different name (repeatn instead of repeat_n) .

Clearly not a high priority but it would be nice to fix this so the names match up.

[cuviper]

Yeah, I agree that we should match repeat_n, deprecating repeatn.