fix(client): handle bare dict/list annotations in construct_type and transform

[kazuki-netizen]

Fixes #1619, #1626, #1628.

Problem

construct_type() and _transform_recursive / _async_transform_recursive index the result of get_args() unconditionally. For an unparameterized annotation, get_args(dict) and get_args(list) return (), so the index access fails whenever a field is annotated as a bare dict or list instead of Dict[K, V] / List[T]:

• construct_type(value={"k": "v"}, type_=dict) → ValueError: not enough values to unpack (expected 2, got 0) (_models.py)
• construct_type(value=["a", "b"], type_=list) → IndexError: tuple index out of range (_models.py)
• transform({"k": "v"}, dict) / async_transform({"k": "v"}, dict) → IndexError: tuple index out of range (_utils/_transform.py)

Fix

Guard each access and fall back to object as the item type when no type parameter is present. This matches the semantics of Dict[str, object] / List[object]: items are returned as-is with no further coercion. Parameterized annotations and the non-mapping / non-list passthrough branches are unchanged.

Verification

• Added regression tests in tests/test_models.py and tests/test_transform.py (sync + async). They fail on main and pass with this change.
• tests/test_models.py + tests/test_transform.py: 122 passed.
• ruff check and ruff format --check clean.

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