Crontab format parsing

Format follows that of the Vixie cron:
https://man7.org/linux/man-pages/man5/crontab.5.html

including support for the following Date-Time matching:
(month AND hour AND minute AND (day-of-month OR day-of-week))

Short 3-letter names for months and week days are supported,
e.g. Jan, Wed.

Sunday's day of week number can be either 0 or 7.

Date-Time entities use java.time.ZonedDateTime for UTC timezone.


Definitions:

field - time and date fragments of the cron entry.

values - each field contains allowed values in the form of single
number or a name, their ranges, ranges with step values, lists, or
an asterisk.

named value - a 3-letter name for a month or a day of week.

range - two numbers or named values separated by a hyphen.

step value - range of values with a given step.

list of values - values separated by comma.