Consistent handling of parsing ns resolution timestamps with and without ciso8601

[ddn0]

I noticed that the behavior of parsing timestamps in aiochclient wrt nanosecond resolution timestamps depends on whether ciso8601 is installed.

import ciso8601
import datetime

ciso8601.parse_datetime('2014-12-05 12:30:45.123456000')
# datetime.datetime(2014, 12, 5, 12, 30, 45, 123456)

datetime.datetime.strptime('2014-12-05 12:30:45.123456000', '%Y-%m-%d %H:%M:%S.%f')
# raises ValueError: unconverted data remains: 000

I understand that using ciso8601 is a performance optimization, but it is a little counterintuitive to me that aiochclient's functional behavior varies due to the present or absence of a library. At the very least, it might be good to document this.

FWIW, for Python >= 3.11, there is a better standard library fallback:

datetime.datetime.fromisoformat('2014-12-05 12:30:45.123456000')
# datetime.datetime(2014, 12, 5, 12, 30, 45, 123456)

Happy to contribute a PR if you give me some guidance as to the expectations of aiochclient around parsing timestamps in general.

Thanks so much for your work!