fix: handle tzinfo=None kwarg in factory.get() without crashing

[frankgoldfish]

Summary

Fixes #1259.

When tzinfo=None is explicitly passed as a keyword argument to arrow.get(), the factory crashed with:

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

Root Cause

In arrow/factory.py, the check:

if len(kwargs) == 1 and tz is None:
    arg_count = 3

incorrectly treats tzinfo=None (explicitly passed) as equivalent to "no tzinfo was passed at all", which forces arg_count = 3 and routes into the positional year/month/day constructor branch — even though no year/month/day args were given.

Fix

Change tz is None to "tzinfo" not in kwargs:

if len(kwargs) == 1 and "tzinfo" not in kwargs:
    arg_count = 3

This correctly distinguishes between:

• tzinfo kwarg absent → old behavior preserved
• tzinfo=None explicitly passed → treated as a valid tzinfo value (defaults to UTC)

Reproduction

import arrow

# Before fix: TypeError
# After fix: works correctly
arrow.get("2025-01-01", "YYYY-MM-DD", tzinfo=None)
# Returns: <Arrow [2025-01-01T00:00:00+00:00]>

Real-world pattern: tzinfo=account.timezone where account.timezone is an optional field that may be None.

Tests

Added test_tzinfo_none_kwargs regression test in tests/test_factory.py. All 49 tests pass.

[frankgoldfish]

Closing this PR — found that PR #1260 already addresses this issue. Apologies for the duplicate.