Switch messages encoding to binary hex - Phase 1

[jpraynaud]

Why

The JSON Hex encoding we use is not very efficient in terms of compression. We want to progressively replace it with a binary encoding in the messages.

What

Replace the JSON Hex encoding to binary encoding in the messages without sudden breaking changes:

• Certificate chain sent to client and aggregator
• Epoch settings sent to signer
• Signer registrations sent to aggregator via REST API
• Signature registrations sent to aggregator:
  • Via REST API
  • Via DMQ

How

• Phase 1: prepare nodes to support binary decoding:
  • Implement IntoBytes/TryFromBytes in the protocol objects
  • Add from_bytes_hex and to_bytes_hex in the ProtocolKey
  • Implement a fallback decoder to binary encoding if JSON Hex encoding fails in the ProtocolKey (ProtocolKeyCodec) on the binary encoding
  • Send signer registrations and signature registrations in binary encoding in signer
  • Store new signer registrations in binary encoding in the signer database (previous will be pruned automatically, no need for migration)
  • Run backward compatibility test
  • Add golden tests for bytes encoding
  • Assess compression gain with new encoding on StmSig and StmAggrSig