More methods on integer traits

[flippette]

Since Rust 1.65.0, there have been a few useful inherent methods that have been added to uN/iN which would be very useful indeed generically (I'll use the Integral/Unsigned/Signed traits here to refer to where they should be added):

Method	MSRV
Integral::{checked_}ilog	1.67.0
Integral::{checked_}ilog2	1.67.0
Integral::{checked_}ilog10	1.67.0
Unsigned::isqrt	1.84.0
Integral::{checked_}next_multiple_of	1.73.0 (uN) / unstable (iN)
Integral::div_ceil	1.73.0 (uN) / unstable (iN)
Integral::div_floor	unstable

Will these be added to funty? Or is the MSRV bump not worth it? And what about a nightly feature flag to opt into yet-unstable functions?