text: Title: Use Griffe's public API
  Body: Any reason you're importing from the internal API?
  
  https://github.com/pydantic/pydantic-ai/blob/b9ec73fe8d47d7859dbf7eefbade198f3cc0eb34/pydantic_ai_slim/pydantic_ai/_griffe.py#L7-L8
  
  You're exposing yourself to breakages if I change these internals :sweat_smile:
  Public equivalent:
  
  ```python
  from griffe import DocstringSectionKind, Docstring, Object as GriffeObject 
  ```
  
  If it's to avoid loading too many things, note that `_griffe.models` imports a lot of stuff anyway:
  
  ```python
  from _griffe.c3linear import c3linear_merge
  from _griffe.docstrings.parsers import DocstringStyle, parse
  from _griffe.enumerations import Kind, ParameterKind, Parser
  from _griffe.exceptions import AliasResolutionError, BuiltinModuleError, CyclicAliasError, NameResolutionError
  from _griffe.expressions import ExprCall, ExprName
  from _griffe.logger import logger
  from _griffe.mixins import ObjectAliasMixin
  ```