Ensure Moment.time() does not lose time zone information

Preserve the tzinfo attribute in Moment.time() by using
datetime.datetime.timetz() instead of datetime.datetime.time().
Improve Moment.time() and Moment.date() performance

...by adding a shortcut that avoids going through Moment.datetime() for
strict conversions without local time zone handling. On CPython, this
makes .date() roughly 3× as fast, and .time() 2× as fast.