feat(runcode): use byte-length instead of string-length
feat(runcode): use byte-length instead of string-length

Co-authored-by: Ondřej Borýsek <c7ee72ea3435fba4f81c5b7507dcda59de3694e2@users.noreply.github.com>
fi-ksi/web-backend,fi-ksi/web-backend