expectedForMonth mirrors chargesForMonth for money that has not moved yet, and
skips confirmed occurrences — those are ordinary purchases that chargesForMonth
has already counted, so counting both would double every settled bill.
The split machinery is extracted rather than duplicated. Two implementations
could round differently or absorb the remainder differently, and the gap would
show up as a penny of drift between the fold's two tracks with no cause the
owner could find. remainderIndexOf and splitPartsOfTotal keep their signatures
as wrappers, so no existing caller changes.
Smaller than planned: 8d2b2ca already made these functions take digits rather
than a currency table, so the shared helper needs no currency plumbing.
Lucas Winther
324b6bd272
