Signed transactions

[Gozala]

Goal

Every transaction should be cryptographically signed via did:key and verifiable.

Deliverable

• Memory spaces are identified by did:key
• Transactions are signed by the memory space did:key or another delegate did:key

⚠️ Here we do not yet verify signatures or that signer is authorized to transact

Dependencies

• Extending transactional guarantees of common-memory #305

[Gozala]

In progress via #433