With period.dynamic: true and period.precision: datetime, running
without --date crashed: compute_next_period() returns a datetime range
(YYYY-MM-DDTHH:MM:SS), which parse_date_range() rejected with a
fullmatch against YYYY-MM-DD only.
parse_date_range now accepts YYYY-MM-DDTHH:MM:SS--YYYY-MM-DDTHH:MM:SS
in addition to plain date ranges, returning datetime strings unchanged
(pass-through, matching compute_next_period output). Mixed-precision
ranges, invalid times and reversed ranges are still rejected with the
existing error messages; date-range behavior is unchanged.
Closes#59
c4ec23048a