Enable class constants

[gordonwatts]

class fork:
    it: int = 10

And then in a lambda expression we should allow for fork.it.

This will also change how enums are done, so this will have far reaching (probably) implications.

[gordonwatts]

Likely this code - where the isinstance for a type is called:

class _rewrite_captured_vars(ast.NodeTransformer):
    def __init__(self, cv: inspect.ClosureVars):
        self._lookup_dict: Dict[str, Any] = dict(cv.nonlocals)
        self._lookup_dict.update(cv.globals)
        self._ignore_stack = []

    def visit_Name(self, node: ast.Name) -> Any:
        if self.is_arg(node.id):
            return node

        if node.id in self._lookup_dict:
            v = self._lookup_dict[node.id]
            if not callable(v):
                # Modules should be sent on down to be dealt with by the
                # backend.
                if not isinstance(v, ModuleType):
                    legal_capture_types = [str, int, float, bool, complex, str, bytes]
                    if type(v) not in legal_capture_types:
                        raise ValueError(
                            f"Do not know how to capture data type '{type(v).__name__}' for "
                            f"variable '{node.id}' - only "
                            f"{', '.join([c.__name__ for c in legal_capture_types])} are "
                            "supported."
                        )
                    return as_literal(v)
            elif isinstance(v, type):
                assert False
        return node