unexpected behavior of `datetime.astimezone` method

Bug report

Bug description:

my system time zone is UTC+04:00

>>> import datetime
>>> datetime.datetime(9999, 12, 31).astimezone() # same for .astimezone(datetime.UTC)
Traceback (most recent call last):
  File "<python-input-46>", line 1, in <module>
    datetime.datetime(9999, 12, 31).astimezone()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
ValueError: year must be in 1..9999, not 10000
>>> datetime.datetime(9999, 12, 31, tzinfo=datetime.UTC).astimezone()
datetime.datetime(9999, 12, 31, 4, 0, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400), '+04'))

same behavior for _pydatetime module, but I found that in version 3.11 the behavior is as next:

>>> datetime.datetime(9999, 12, 31).astimezone()
datetime.datetime(9999, 12, 31, 0, 0, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400), '+04'))

EDIT: same behavior for datetime(1, 1, 1):

>>> datetime.datetime(1, 1, 1).astimezone()
Traceback (most recent call last):
  File "<python-input-23>", line 1, in <module>
    datetime.datetime(1, 1, 1).astimezone()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
ValueError: year must be in 1..9999, not 0

CPython versions tested on:

CPython main branch, 3.13, 3.12

Operating systems tested on:

Linux

Linked PRs

• gh-130752

Start with the datetime.astimezone entry point and reproduce the reported year-1 and year-9999 cases on CPython main, comparing them with Python 3.11 behavior. Review linked PR gh-130752 before proceeding; the work is done when the boundary cases no longer raise unexpectedly and the intended behavior is covered by the relevant tests.