Make bitset `would_modify_words` more vectorizer-friendly Currently this function compares a single pair of `u64` at a time, which is potentially slower than comparing multiple words before each early-exit check, especially for the large chunks used by ChunkedBitSet. Perf shows a notable improvement in `cranelift-codegen`, which is the one benchmark that is known to stress these code paths. - Incorporates https://github.com/rust-lang/rust/pull/153759.