fix Type Narrowing Depends on Order of Keyword Arguments #4187

[asukaminato0721]

Summary

Fixes #4187

Updated subtype inference to preserve quantified types when a union contains a bare inference variable, preventing argument-order-dependent widening to the TypeVar bound.

Test Plan

add test

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

apprise (https://github.com/caronc/apprise)
- ERROR apprise/plugins/vapid/__init__.py:356:20-43: Object of class `dict` has no attribute `load` [missing-attribute]
- ERROR apprise/plugins/vapid/__init__.py:391:16-22: `not in` is not supported between `object` and `WebPushSubscriptionManager` [unsupported-operation]
- ERROR apprise/plugins/vapid/__init__.py:405:28-65: Argument `EllipticCurvePublicKey | Unknown | None` is not assignable to parameter `public_key` with type `EllipticCurvePublicKey` in function `apprise.utils.pem.ApprisePEMController.encrypt_webpush` [bad-argument-type]
- ERROR apprise/plugins/vapid/__init__.py:405:47-53: Cannot index into `WebPushSubscriptionManager` [bad-index]
- ERROR apprise/plugins/vapid/__init__.py:406:29-67: Argument `bytes | Unknown | None` is not assignable to parameter `auth_secret` with type `bytes` in function `apprise.utils.pem.ApprisePEMController.encrypt_webpush` [bad-argument-type]
- ERROR apprise/plugins/vapid/__init__.py:406:48-54: Cannot index into `WebPushSubscriptionManager` [bad-index]
- ERROR apprise/plugins/vapid/__init__.py:609:42-70: Argument `bytes | None` is not assignable to parameter `data` with type `bytes` in function `apprise.utils.base64.base64_urlencode` [bad-argument-type]

xarray (https://github.com/pydata/xarray)
- ERROR xarray/backends/api.py:1369:48-63: Argument `set[_FLike]` is not assignable to parameter `paths_to_remove` with type `set[ReadBuffer[Unknown] | _FLike]` in function `_remove_path` [bad-argument-type]
- ERROR xarray/backends/api.py:1371:31-44: Argument `NestedSequence[ReadBuffer[Unknown] | _FLike]` is not assignable to parameter `object` with type `NestedSequence[_FLike] | _FLike` in function `list.append` [bad-argument-type]
+ ERROR xarray/core/variable.py:470:27-31: Argument `Buffer | _NestedSequence[bytes | complex | str] | _NestedSequence[_SupportsArray[dtype]] | _SupportsArray[dtype] | bytes | complex | str | T_DuckArray` is not assignable to parameter `new_data` with type `_arrayapi[Any, Unknown] | _arrayfunction[Any, Unknown]` in function `xarray.namedarray.core.NamedArray._check_shape` [bad-argument-type]
+ ERROR xarray/core/variable.py:471:22-26: `Buffer | _NestedSequence[bytes | complex | str] | _NestedSequence[_SupportsArray[dtype]] | _SupportsArray[dtype] | bytes | complex | str | T_DuckArray` is not assignable to attribute `_data` with type `_arrayapi[Any, Unknown] | _arrayfunction[Any, Unknown]` [bad-assignment]