Refactor / understand start of `make_scalar_integer`

[codereport]

In jsrc/verbs/monadic/tally.cpp:

make_scalar_integer(J jt, int64_t k) -> array {
    if (xor_replicate_sign(k) <= NUMMAX) {
        return !zero_or_one(k) ? refactorme_num(k) : zeroionei(k);
    }