I see use bytes; without any utf8::upgrade or utf8::downgrade, and that usually indicates code that suffers from "The Unicode Bug".

sub bytelen(_) {
    require bytes;
    return bytes::length($_[0]);
}
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should be

sub utf8len(_) {
    utf8::upgrade($_[0]);
    require bytes;
    return bytes::length($_[0]);
}
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Or the same without bytes:

sub utf8len(_) {
    utf8::upgrade($_[0]);
    Encode::_utf8_off($_[0]);
    my $utf8len = length($_[0]);
    Encode::_utf8_on($_[0]);
    return $utf8len;
}
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Update: Added non-bytes alternative.