Closes #3502

Problem

A bare, unparameterised typing.List / typing.Tuple field crashes to_arrow_schema with an opaque AttributeError: __args__:

from typing import Tuple
from lancedb.pydantic import LanceModel

class Doc(LanceModel):
    items: Tuple

Doc.to_arrow_schema()  # AttributeError: __args__

In _py_type_to_arrow_type, the branch elif getattr(py_type, "__origin__", None) in (list, tuple) is taken for a bare generic (its __origin__ is list / tuple), but the next line reads py_type.__args__[0], and a bare generic has no __args__. Other unsupported types (e.g. Dict[str, int]) correctly raise a clear TypeError, so this case is inconsistent.

Fix

Guard the element-type lookup with getattr(py_type, "__args__", None) and raise a clear TypeError when it is missing, matching the existing behavior for other unsupported types. Bare builtin list / tuple are unaffected (their __origin__ is None, so they already fall through to the existing TypeError).

Testing

• Added test_bare_generic_raises_type_error covering both List and Tuple.
• ruff format and ruff check clean.