proof: enable early termination of the universe proof courier

[Roasbeef]

Today we can use the Universe tree and the gRPC/REST API as a source for issuance and transfer proofs. The main loop walks backwards from the transaction is received on chain, using the prev outpoints to look up the next leaf in the Universe trees:

taproot-assets/proof/courier.go

Lines 1045 to 1095 in a990fdf

	for {
	assetID := *loc.AssetID
	universeID := unirpc.MarshalUniverseID(assetID[:], nil)
	assetKey := unirpc.MarshalAssetKey(
	*loc.OutPoint, &loc.ScriptKey,
	)
	universeKey := unirpc.UniverseKey{
	Id: universeID,
	LeafKey: assetKey,
	}
	resp, err := c.client.QueryProof(ctx, &universeKey)
	if err != nil {
	return nil, err
	}
	// Decode transition proof from query response.
	proofBlob := resp.AssetLeaf.IssuanceProof
	var transitionProof Proof
	if err := transitionProof.Decode(
	bytes.NewReader(proofBlob),
	); err != nil {
	return nil, err
	}
	revProofs = append(revProofs, transitionProof)
	// Break if we've reached the genesis point (the asset is the
	// genesis asset).
	asset := transitionProof.Asset
	if asset.IsGenesisAsset() {
	break
	}
	// Update locator with principal input to the current outpoint.
	prevID, err := transitionProof.Asset.PrimaryPrevID()
	if err != nil {
	return nil, err
	}
	// Parse script key public key.
	scriptKeyPubKey, err := btcec.ParsePubKey(prevID.ScriptKey[:])
	if err != nil {
	return nil, fmt.Errorf("failed to parse script key "+
	"public key from Proof.PrevID: %w", err)
	}
	loc.ScriptKey = *scriptKeyPubKey
	loc.AssetID = &prevID.ID
	loc.OutPoint = &prevID.OutPoint
	}

Each time we use the gRPC client to query for the proof. Instead, we should add a step right before that, that attempts to look in the local proof acrhive. This'll allow us to short circuit, as all assets with the same asset ID eventually have a common ancestor. Once we know about this ancestor, then we have the rest of the proof so we can exit early.

Steps To Completion

• Pass in the proof archive into the UniverseRpcCourier. Use that local archive to query before making a network query to the universe.