Allow class/function calls in list assignments

[BPHarris]

The following minimal example fails on rattr main but should pass. This fails as visit_ClassAssign expects that all assignments with a class in the RHS will be one-to-one.

Support for many-to-many may be out of scope (see footnote), but the simplest case below should pass.

class MyClass:
    pass

def in_init():
    my_list = [MyClass()]

def in_concat():
    my_list = []
    my_list += [MyClass()]

Footnote

In short the issue is that many-to-many involves implicit unpacking (which is runtime so out-of-scope) and in python we can get rather yucky with it, take this for example:

In [1]: class MyClass:
   ...:     def __new__(cls):
   ...:         return [1, 2]
   ...: 
   ...: a, b = [*MyClass()]

In [2]: a
Out[2]: 1

In [3]: b
Out[3]: 2

[BPHarris]

Specifically the example code in the issue gives this failure:

When ideally we should visit the calls in the list, and give a warning if needed but not a fatal error.