Extend judy_128_map with iterator helpers

[knutin]

This PR includes some extra methods in judy_128_map which allows iterating over the array without using j128m_fold. The API works exactly like the normal Judy API, except that you need to explicitly pass references.

__uint128_t idx = 0;
PWord_t pv = NULL;
j128m_find(&jm, &pv, &idx);
while (pv != NULL) {
    /* Do something with *pv */
     j128m_next(&jm, &pv, &idx);
}

[CLAassistant]

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[tuulos]

@knutin I guess j128_del doesn't exist so this can be removed?

[oavdeev]

It does, at least in some local branch I was using it, let me see..