Add a sink operation to avoid dangling nodes

Closes #132 (closed)

Adds a sink operation

No tests were added because I didn't think there was a nice way to test something that does "nothing".

b_asic/core_operations.py

@@ -1278,7 +1278,6 @@ class Sink(AbstractOperation):
 
     _execution_time = 0
     is_linear = True
-    is_constant = True
 
     def __init__(self, name: Name = ""):
         """Construct a Sink operation."""
@@ -1294,7 +1293,7 @@ class Sink(AbstractOperation):
         return TypeName("sink")
 
     def evaluate(self):
-        return self.param("value")
+        raise NotImplementedError
 
     @property
     def latency(self) -> int: