RFE: use zoneinfo instead of pytz

[kloczek]

Switch to standard zoneinfo module.
Below may help pydantic/pydantic-core@fd262933

[tkloczko@pers-jacek dirty-equals-0.7.1]$ grep -r pytz
dirty_equals/_datetime.py:    Instantiate a `ZoneInfo` object from a string, falling back to `pytz.timezone` when `ZoneInfo` is not available
dirty_equals/_datetime.py:            import pytz
dirty_equals/_datetime.py:            raise ImportError('`pytz` or `zoneinfo` required for tz handling') from e
dirty_equals/_datetime.py:            return pytz.timezone(tz)  # type: ignore[return-value]
dirty_equals/_datetime.py:                (or `pytz.timezone` on 3.8) to get a timezone,
requirements/linting.in:types-pytz
requirements/linting.txt:types-pytz==2023.3.1.1
requirements/tests.in:pytz
requirements/tests.txt:pytz==2023.3.post1
tests/test_datetime.py:import pytz
tests/test_datetime.py:            pytz.timezone('Europe/London').localize(datetime(2022, 2, 15, 15, 15)),
tests/test_datetime.py:                approx=pytz.timezone('America/New_York').localize(datetime(2022, 2, 15, 10, 15)), enforce_tz=False
tests/test_datetime.py:            pytz.timezone('Europe/London').localize(datetime(2022, 2, 15, 15, 15)),
tests/test_datetime.py:            IsDatetime(approx=pytz.timezone('America/New_York').localize(datetime(2022, 2, 15, 10, 15))),

[samuelcolvin]

We'll have to continue to use pytz until we drop support for 3.8. are you sure it makes sense to switch now.

[kloczek]

Pointed commit shows how to handle 3.8 (plus my comment pydantic/pydantic-core@fd262933#r142482296)

[samuelcolvin]

PR welcome to adopt zoneinfo.