[consensus/threshold-simplex] Store Deserialized Partial Signature to Avoid Duplicate Deserialization

[patrick-ogrady]

In the current consensus code, we drop deserialized partial signatures and re-deserialize them when generating a notarization, nullification, or finalization:

• monorepo/consensus/src/threshold_simplex/actors/voter/actor.rs

  Lines 1037 to 1080 in eaedda6

  	// Verify signature
  	let Some(signature) = Eval::deserialize(&nullify.view_signature) else {
  	debug!(
  	public_key_index,
  	"partial signature is not formatted correctly"
  	);
  	return;
  	};
  	if signature.index != public_key_index {
  	debug!(
  	public_key_index,
  	partial_signature = signature.index,
  	"invalid signature index for nullify"
  	);
  	return;
  	}
  	let nullify_message = nullify_message(nullify.view);
  	if ops::partial_verify_message(
  	identity,
  	Some(&self.nullify_namespace),
  	&nullify_message,
  	&signature,
  	)
  	.is_err()
  	{
  	return;
  	}
  	// Verify seed
  	let Some(seed) = Eval::deserialize(&nullify.seed_signature) else {
  	return;
  	};
  	if seed.index != public_key_index {
  	return;
  	}
  	let seed_message = seed_message(nullify.view);
  	if ops::partial_verify_message(identity, Some(&self.seed_namespace), &seed_message, &seed)
  	.is_err()
  	{
  	return;
  	}
  	// Handle nullify
  	self.handle_nullify(public_key_index, nullify).await;

• monorepo/consensus/src/threshold_simplex/actors/voter/actor.rs

  Lines 450 to 454 in eaedda6

  	for notarize in notarizes.values() {
  	let eval = Eval::deserialize(&notarize.message.proposal_signature).unwrap();
  	notarization.push(eval);
  	let eval = Eval::deserialize(&notarize.message.seed_signature).unwrap();
  	seed.push(eval);

We should find a way to store arbitrary fixed-size arrays with a parsed protobuf object or find a way to parse the types directly with prost (#454).

We currently have Parsed but that is typically only used with Digests (and support one associated item):

monorepo/consensus/src/lib.rs

Lines 31 to 36 in eaedda6

	/// Parsed is a wrapper around a message that has a parsable digest.
	#[derive(Clone)]
	struct Parsed<Message, D: Digest> {
	pub message: Message,
	pub digest: D,
	}

[patrick-ogrady]

Related #489