policy property Null safety

1. jrpn
2. model
3. Memory<OT extends ProgramOperation>
4. policy property

Memory class

1. Constructors
2. Memory
3. Properties
4. hashCode
5. model
6. policy
7. program
8. programNybbles
9. registers
10. runtimeType
11. storage
12. totalNybbles
13. Methods
14. decodeJson
15. initializeSystem
16. noSuchMethod
17. reset
18. toJson
19. toString
20. Operators
21. operator ==