rpcutils: move RFQ gRPC marshal functionality from taprpc

Move RFQ related gRPC marshalling functionality from the taprpc package
to the rpcutils package as preparation for future modularization.

Author: ffranr

rpcserver.go

@@ -7616,7 +7616,7 @@ func (r *rpcServer) SendPayment(req *tchrpc.SendPaymentRequest,
 		}
 
 		// Unmarshall the accepted quote's asset rate.
-		assetRate, err := rfqrpc.UnmarshalFixedPoint(
+		assetRate, err := rpcutils.UnmarshalRfqFixedPoint(
 			acceptedQuote.BidAssetRate,
 		)
 		if err != nil {
@@ -7777,7 +7777,7 @@ func (r *rpcServer) parseRequest(
 func checkOverpayment(quote *rfqrpc.PeerAcceptedSellQuote,
 	paymentAmount lnwire.MilliSatoshi, allowOverpay bool) error {
 
-	rateFP, err := rfqrpc.UnmarshalFixedPoint(quote.BidAssetRate)
+	rateFP, err := rpcutils.UnmarshalRfqFixedPoint(quote.BidAssetRate)
 	if err != nil {
 		return fmt.Errorf("cannot unmarshal asset rate: %w", err)
 	}
@@ -8118,7 +8118,7 @@ func validateInvoiceAmount(acceptedQuote *rfqrpc.PeerAcceptedBuyQuote,
 	// that we need to pay. We can now update the invoice with this amount.
 	//
 	// First, un-marshall the ask asset rate from the accepted quote.
-	askAssetRate, err := rfqrpc.UnmarshalFixedPoint(
+	askAssetRate, err := rpcutils.UnmarshalRfqFixedPoint(
 		acceptedQuote.AskAssetRate,
 	)
 	if err != nil {

taprpc/rfqrpc/marshal.go renamed to rpcutils/rfq_marshal.go

@@ -1,14 +1,17 @@
-package rfqrpc
+package rpcutils
 
 import (
 	"fmt"
 	"math/big"
 
 	"github.com/lightninglabs/taproot-assets/rfqmath"
+	"github.com/lightninglabs/taproot-assets/taprpc/rfqrpc"
 )
 
-// UnmarshalFixedPoint converts an RPC FixedPoint to a BigIntFixedPoint.
-func UnmarshalFixedPoint(fp *FixedPoint) (*rfqmath.BigIntFixedPoint, error) {
+// UnmarshalRfqFixedPoint converts an RPC FixedPoint to a BigIntFixedPoint.
+func UnmarshalRfqFixedPoint(fp *rfqrpc.FixedPoint) (*rfqmath.BigIntFixedPoint,
+	error) {
+
 	// Return an error is the scale component of the fixed point is greater
 	// than the max value of uint8.
 	if fp.Scale > 255 {