always format into pythonic class name

[DaanRademaker]

Open to more suggestions to always format into proper class name format

[dan1elt0m]

I like the idea. However, not sure whether this works for subclasses. Can you add a test where this is done for a subclass? I would say changing the class name in the registry itself breaks the typing reference in the parent. e.g., below Hello_World example:

class HelloWorld(BaseModel):
    a: int

class A (BaseModel):
    a: Hello_World

If it breaks, then the formatting needs to happen before add_class is called