Add pydantic compatibility

[07pepa]

Why: pydantic is useful for validation and settings and sometimes it is usefull to store stuff like Locale/date time pattern in setting

it would be possible to extend babel with optional pydantic compatibility when pydantic and pydantic core would be tried to be imported and a extra magic dunder method would be created __get_pydantic_core_schema__ that would use preexisting methods for parsing validation and serialization

non user would se maybe slight slow down on import (and exception handling in imports)