Auto merge of #143540 - yotamofek:pr/library/simplify-num-fmt, r=tgross35

Simplify num formatting helpers

Noticed `ilog10` was being open-coded when looking at this diff: https://github.com/rust-lang/rust/pull/143423/files/85d6768f4c437a0f3799234df20535ff65ee17c2..76d9775912ef3a7ee145053a5119538bf229d6e5#diff-6be9b44b52d946ccac652ddb7c98146a01b22ea0fc5737bc10db245a24796a45
That, and two other small cleanups 😁

(should probably go through perf just to make sure it doesn't regress formatting)

Author: bors