Support general durations for time offsets in the same way python datetime does

[joekiller]

This is a request to support general durations for time offsets to enable pydantic/pydantic#12049.

Currently the Datetime Types type only accept datetimes with hours and minutes while python and 8601 strings support general durations for time offsets that include seconds.

pydantic form: YYYY-MM-DD[T]HH:MM[:SS[.ffffff]][Z or [±]HH[:]MM]
python 3.9 forms:

• YYYY-MM-DD[*HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]] via datetime.fromisoformat
• %z UTC offset in the form ±HHMM[SS[.ffffff]] (empty string if the object is naive) via strftime() and strptime() Format Codes

We've had some timestamps come in with the general durations that included seconds and it blows us up. Supporting the general durations with greater precision is desired.