TypedPython: compile methods of fixed-layout classes (N-11 remainder) #155

SPEC N-11 is implemented for module-level functions; methods are planned (self guarded type(self) is C, the same per-access class checks as #124). Today every method stays interpreted, so object-oriented code only benefits through free functions.

Done when: methods of an N-11 class compile, self with a subclass instance deopts or takes the generic path exactly like a Param.cls parameter, bound-method calls from interpreted code and C-to-C calls from compiled code both work, and the class-change scenarios of test_cgen_class_changes.py pass for methods too.