Summary

• avoid indexing get_args() when request transform sees a bare dict annotation
• avoid unpacking empty get_args() in construct_type(..., type_=dict)
• add regressions for sync/async transform and model construction with unparameterized dict

Fixes #3338.
Fixes #3341.

Tested

• Reproduced both failures locally before the patch with PYTHONPATH=src.
• python -m pytest tests\test_transform.py::test_bare_dictionary_annotation tests\test_transform.py::test_dictionary_items tests\test_models.py::test_construct_bare_dict_type -q
• python -m pytest tests\test_transform.py tests\test_models.py -q
• python -m py_compile src\openai\_utils\_transform.py src\openai\_models.py tests\test_transform.py tests\test_models.py
• python -m ruff check src\openai\_utils\_transform.py src\openai\_models.py tests\test_transform.py tests\test_models.py
• python -m ruff format --check src\openai\_utils\_transform.py src\openai\_models.py tests\test_transform.py tests\test_models.py
• git diff --check