[WIP] Implement subroutine opcodes

Author: Peppece

eth/vm/logic/flow.py

@@ -68,7 +68,7 @@ def beginsub(computation: BaseComputation) -> None:
 
 def jumpsub(computation: BaseComputation) -> None:
     sub_loc = computation.stack_pop1_int()
-    code_range_length = computation.code._length_cache
+    code_range_length = computation.code.__len__()
 
     if sub_loc >= code_range_length:
         raise InvalidJumpDestination(