fix: guard against IndexError/ValueError when dict annotation has no type args

[adhavan18]

Fixes #3338 and #3341.

Problem

get_args(dict) returns an empty tuple when the annotation is a bare, unparameterised dict (no [K, V]). Two places assumed there are always two args:

• _transform.py: get_args(stripped_type)[1] → IndexError
• _models.py: _, items_type = get_args(type_) → ValueError

Minimal reproducer:

from typing import TypedDict
from openai._utils._transform import transform

class Params(TypedDict, total=False):
    metadata: dict  # bare dict, no [K, V]

transform({'metadata': {'key': 'val'}}, Params)  # IndexError

Fix

Check len(args) >= 2 before indexing; return early without transformation when the annotation is unparameterised.

Test

All existing tests pass. New test added for bare dict annotation.