Ensure Mainnet state is migratable

[turbolent]

Issue To Be Solved

While optimizing the storage format #738, make sure we keep being able to migrate all of the Mainnet state once we are done with the format changes.

Suggested Solution

Add functionality to the state decoding tool to use the old decoder (v3), then encode and decode using the new encoder and new decoder (v4), and finally compare the final value to the initially decoded value.

This requires storable values to be comparable.

Definition of Done

• Extend state decoding tool with
  • Support for decoding using pre-v4 format
  • Support for re-encoding and decoding initially decoded data
  • Comparsion of initially decoded value and values that was re-encoded and decoded
• Implement equality for storable values