Added slots to non-gui modules

Gave all non gui classes slots. I think we should wait with slots for gui classes until we've made tests for them.

Closes #27 (closed)

src/simudator/core/modules/demux.py

@@ -30,6 +30,8 @@ class Demux(Module):
         Initial value to output to the currently selected output signal.
     """
 
+    __slots__ = ("_bit_length", "_value")
+
     def __init__(
         self,
         control: Signal,