Covenant-less TxBuilder (#178)

* initial commit

* wip

* add bitcointree pkg in common

* add bitcoin txbuilder

* fix BuildPoolTx test

* fix sweeper

* v0 musig2 congestion tree

* bitcointree: add signatures support

* add Makefile in common

* fix lint

* fix go.mod and TxBuilder

* go mod tidy

* rename "pset" --> "psbt"

* add GetSweepInput method in TxBuilder

* fix extractSweepLeaf (bitcoin tx builder)

server/internal/core/application/service.go

@@ -395,9 +395,10 @@ func (s *service) startFinalization() {
 		log.WithError(err).Warn("failed to create pool tx")
 		return
 	}
-
 	log.Debugf("pool tx created for round %s", round.Id)
 
+	// TODO BTC make the senders sign the tree
+
 	connectors, forfeitTxs, err := s.builder.BuildForfeitTxs(s.pubkey, unsignedPoolTx, payments, s.minRelayFee)
 	if err != nil {
 		changes = round.Fail(fmt.Errorf("failed to create connectors and forfeit txs: %s", err))