Add `ilog10` result range hints
This PR adds hints that the return value of `T::ilog10` will never exceed `T::MAX.ilog10()`.
This works because `ilog10` is a monotonically nondecreasing function, the maximum return value is reached at the max input value.
Similar to how this helps in `slice::Iter::position`, LLVM sometimes loses track of how high this can get, so for `TrustedLen` iterators tell it what the upper bound is.
