fix: treat explicit tzinfo=None as not provided in ArrowFactory.get()

[AKIB473]

Fixes #1259

Problem

arrow.get('2025-01-01', 'YYYY-MM-DD', tzinfo=None) crashed with:

TypeError: Arrow.__init__() missing 1 required positional argument: 'day'

The root cause is in ArrowFactory.get():

# tzinfo kwarg is not provided
if len(kwargs) == 1 and tz is None:
    arg_count = 3

When tzinfo=None is passed explicitly, len(kwargs) == 1 is True and tz is None is also True, so arg_count is set to 3 and the call falls into the 3+ arg constructor path — crashing because '2025-01-01' and 'YYYY-MM-DD' are not valid year/month/day integers.

The intent of the check was to detect that no tzinfo keyword was provided at all, not to check whether the value is None.

Fix

Change the condition to check key presence:

# tzinfo kwarg is not provided (explicit tzinfo=None is treated as not provided)
if len(kwargs) == 1 and "tzinfo" not in kwargs:
    arg_count = 3

This means tzinfo=None is now treated identically to omitting tzinfo — which is the intuitive behaviour when tzinfo comes from an optional field that can be None.

Tests

Two regression tests added to tests/test_factory.py:

• test_two_args_str_str_tzinfo_none — arrow.get('2025-01-01', 'YYYY-MM-DD', tzinfo=None) must parse correctly
• test_no_args_tzinfo_none — arrow.get(tzinfo=None) must return current UTC time