Resolve PEP 695 type alias in the union unpacker

[uttam12331]

Fixes #343.

Problem

A PEP 695 type alias used as a member of a union field serializes fine but fails to deserialize — from_dict raises InvalidFieldValue for every value, so the type no longer round-trips:

type ScalarAlias = int

@dataclass
class MyClass(DataClassDictMixin):
    x: "ScalarAlias | list[int]"

MyClass(1).to_dict()             # {'x': 1}   -- ok (fixed in #336)
MyClass.from_dict({"x": 1})      # InvalidFieldValue
MyClass.from_dict({"x": [1, 2]}) # InvalidFieldValue

Cause

UnionUnpackerBuilder._add_body builds the type-match condition from the raw member's __name__:

condition = f"type(value) is {type_arg.__name__}"

For a TypeAliasType, __name__ is the alias name ("ScalarAlias"), which is not bound in the generated code's namespace. The emitted line becomes type(value) is ScalarAlias, raising NameError before any working branch is reached — and since from_dict converts exceptions into InvalidFieldValue, the alias member breaks the entire union, not just its own branch.

Fix

Resolve the alias to its underlying type before taking __name__, exactly as the packer side already does (resolve_type_alias_type, added in #336):

match_type = resolve_type_alias_type(type_arg)
...
condition = f"type(value) is {match_type.__name__}"

resolve_type_alias_type is a no-op for non-alias types and on Python < 3.12, so this is safe on all supported versions.

Tests

Added test_type_alias_type_with_union_value_unpacker mirroring the existing ..._packer test but asserting from_dict. It fails on master (InvalidFieldValue) and passes with the fix. The union / PEP 695 / recursive-union / discriminated-union suites pass (161 passed). black, ruff, and mypy are clean on the change.