specs: PQ signatures

[unnawut]

[unnawut]

Partially complete by leanEthereum/leanSpec#67 and leanEthereum/leanSpec#92

Remaining work:

• Actually signing & verifying as part of the specs
• Confirm the hash-sig reference code & parameters to target for devnet1
  • i.e. there was a hint that the signature size will go up from 3100 bytes earlier to ~4000 bytes but exact value and reference code is TBC -> remains at 3100 bytes