changed how CallableGroup works - now every add adds a CancellableCallback

  and it's always true that CallableGroup has it's own cancellable callbacks.

satella/coding/concurrent/callablegroup.py

@@ -4,11 +4,10 @@ import time
 import typing as tp
 
 from satella.coding.deleters import DictDeleter
-from satella.coding.structures.mixins import HashableMixin
 from satella.coding.typing import T, NoArgCallable
 
 
-class CancellableCallback(HashableMixin):
+class CancellableCallback:
     """
     A callback that you can cancel.
 
@@ -36,6 +35,12 @@ class CancellableCallback(HashableMixin):
         self.callback_fun = callback_fun
         self.cancelled = False
 
+    def __hash__(self):
+        return hash(self.id)
+
+    def __eq__(self, other) -> bool:
+        return hash(self) == hash(other)
+
     def __call__(self, *args, **kwargs):
         if not self.cancelled:
             return self.callback_fun(*args, **kwargs)