chanbackup: add Single.CloseTxInputs field

The field is optional. It stores inputs needed to produce signed commit tx using
chantools scbforceclose, which calls function GetSignedCommitTx. New backups
have this field filled if commit tx is available (for all cases except when DLP
is active). If a backup has this data, the field is filled from it, otherwise it
is kept empty.

Modified test function genRandomOpenChannelShell to cover new types of channels
(simple taproot channel and custom channel) and to cover combinations of bits.
Make sure that TapscriptRoot field is properly packed and unpacked.

chanbackup/pubsub.go

@@ -267,9 +267,10 @@ func (s *SubSwapper) backupUpdater() {
 				log.Debugf("Adding channel %v to backup state",
 					newChan.FundingOutpoint)
 
-				s.backupState[newChan.FundingOutpoint] = NewSingle(
+				single := NewSingle(
 					newChan.OpenChannel, newChan.Addrs,
 				)
+				s.backupState[newChan.FundingOutpoint] = single
 			}
 
 			// For all closed channels, we'll remove the prior