Rename PyMethodsImpl -> PyMethods

[kngwyu]

As I'll introduce PyProtoMethods, I renamed PyMethodsImple for consistent naming.

[kngwyu]

Actions says

running 1 test
ERROR: failed to read cargo metadata: EOF while parsing a value at line 1 column 0

Wow.

[davidhewitt]

How about just having one trait maybe called PyClassMembers with py_methods() and py_proto_methods()? Maybe this isn't possible if PyProtoMethods won't always be implemented.

I don't have strong opinion though so please continue with two traits if you prefer to keep them separate!

[kngwyu]

just having one trait maybe called PyClassMembers

I think it's possible but can be confusing since PyProtoMethods has many methods like:

pub trait PyProtoMethods {
    fn basic_methods() -> Option<NonNull<PyObjectMethods>> {
        None
    }
    fn buffer_methods() -> Option<NonNull<PyBufferProcs>> {
        None
    }
    fn descr_methods() -> Option<NonNull<PyDescrMethods>> {
        None
    }
...
}