opcode: implement some read/write state ops #30
Description
related to #21, probably would be good to introduce some operations to read/write some state to store:
- anti-replay counters
- generation/epoch counters
- (maybe) hash of some state
We should have a clear, concrete use case before implementing a generic interface (that might be overkill). Priority should be to get it as simple as possible to make analysis easy.
Some primitive to provide access to NVRAM in some HSMs.