Update types of values passed to `:set()` and parse()

[TarantoolBot]

:set() can accept only integer values for year, month,
day, hour, min, sec, usec, msec and nsec.
The type of tzoffset can be integer or string, timestamp can
be integer or double. tzoffset passed to datetime.parse()
can be integer or string.
Requested by @ligurio in tarantool/tarantool@6e77907.