objfun.c

Returns a tuple that is somewhat compatible to inspect.FullArgSpec():

 * args: implemented
 * varargs: implemented (either None or "args")
 * varkw: implemented (either None or "kwargs")
 * defaults: not implemented, always None (not too difficult tbh)
 * kwonlyargs: implemented
 * kwonlydefaults: not implemented, always None
 * annotations: not implemented, always None

Inspired by mp_setup_code_state_helper() in bc.c which is the function
that reads the prelude of the bytecode to prepare a function to be
called, and also is the function that raises TypeError when you call it
wrong.

MP_BC_PRELUDE_SIG_DECODE() and MP_BC_PRELUDE_SIZE_DECODE() are two
macros that put a bunch of variables in your function, that's where all
the n_*_args variables come from.