unsafe fn searcher_kind_one_byte(
    searcher: &Searcher,
    _prestate: &mut PrefilterState,
    haystack: &[u8],
    _needle: &[u8],
) -> Option<usize> {
    let needle = searcher.kind.one_byte;
    crate::memchr(needle, haystack)
}
Reads from the `one_byte` field of `SearcherKind` to handle the case of
searching for a single byte needle. Works on all platforms.

# Safety

Callers must ensure that the `searcher.kind.one_byte` union field is set.
src/memmem/searcher.rs