fix(pydantic): Remove pydantic.v1 imports for Python 3.14 compatibility
When using Pydantic V2 on Python 3.14+, the compat module was importing
from pydantic.v1 which triggers a warning:
"Core Pydantic V1 functionality isn't compatible with Python 3.14 or greater."
Changes:
- Import lenient_issubclass and smart_deepcopy from pydantic._internal._utils
instead of pydantic.v1.utils (works on all Python versions with Pydantic V2)
- On Python 3.14+, define is_new_type locally instead of importing from
pydantic.v1.typing
Fixes #4043