multi: upgrade new taproot TLVs to use tlv.OptionalRecordT

In this commit, we update new Taproot related TLVs (nonces, partial sig,
sig with nonce, etc). Along the way we were able to get rid of some
boiler plate, but most importantly, we're able to better protect against
API misuse (using a nonce that isn't initialized, etc) with the new
options API. In some areas this introduces a bit of extra boiler plate,
and where applicable I used some new helper functions to help cut down
on the noise.

Note to reviewers: this is done as a single commit, as changing the API
breaks all callers, so if we want things to compile it needs to be in a
wumbo commit.

lnwire/closing_signed.go

@@ -36,7 +36,7 @@ type ClosingSigned struct {
 	//
 	// NOTE: This field is only populated if a musig2 taproot channel is
 	// being signed for. In this case, the above Sig type MUST be blank.
-	PartialSig *PartialSig
+	PartialSig OptPartialSigTLV
 
 	// ExtraData is the set of data that was appended to this message to
 	// fill out the full maximum transport message size. These fields can
@@ -76,17 +76,15 @@ func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
 		return err
 	}
 
-	var (
-		partialSig PartialSig
-	)
+	partialSig := c.PartialSig.Zero()
 	typeMap, err := tlvRecords.ExtractRecords(&partialSig)
 	if err != nil {
 		return err
 	}
 
 	// Set the corresponding TLV types if they were included in the stream.
-	if val, ok := typeMap[PartialSigRecordType]; ok && val == nil {
-		c.PartialSig = &partialSig
+	if val, ok := typeMap[c.PartialSig.TlvType()]; ok && val == nil {
+		c.PartialSig = tlv.SomeRecordT(partialSig)
 	}
 
 	if len(tlvRecords) != 0 {
@@ -102,9 +100,9 @@ func (c *ClosingSigned) Decode(r io.Reader, pver uint32) error {
 // This is part of the lnwire.Message interface.
 func (c *ClosingSigned) Encode(w *bytes.Buffer, pver uint32) error {
 	recordProducers := make([]tlv.RecordProducer, 0, 1)
-	if c.PartialSig != nil {
-		recordProducers = append(recordProducers, c.PartialSig)
-	}
+	c.PartialSig.WhenSome(func(sig PartialSigTLV) {
+		recordProducers = append(recordProducers, &sig)
+	})
 	err := EncodeMessageExtraData(&c.ExtraData, recordProducers...)
 	if err != nil {
 		return err