feat: TX proposal procedures attribute

This adds support for decoding and retrieving governance proposal
procedures from a TX

Fixes #344

ledger/conway.go

@@ -121,10 +121,10 @@ func (h *ConwayBlockHeader) Era() Era {
 
 type ConwayTransactionBody struct {
 	BabbageTransactionBody
-	TxVotingProcedures   VotingProcedures `cbor:"19,keyasint,omitempty"`
-	ProposalProcedures   *cbor.Value      `cbor:"20,keyasint,omitempty"`
-	CurrentTreasuryValue int64            `cbor:"21,keyasint,omitempty"`
-	Donation             uint64           `cbor:"22,keyasint,omitempty"`
+	TxVotingProcedures   VotingProcedures    `cbor:"19,keyasint,omitempty"`
+	TxProposalProcedures []ProposalProcedure `cbor:"20,keyasint,omitempty"`
+	CurrentTreasuryValue int64               `cbor:"21,keyasint,omitempty"`
+	Donation             uint64              `cbor:"22,keyasint,omitempty"`
 }
 
 func (b *ConwayTransactionBody) UnmarshalCBOR(cborData []byte) error {
@@ -176,6 +176,157 @@ type GovActionId struct {
 	GovActionIdx  uint32
 }
 
+type ProposalProcedure struct {
+	cbor.StructAsArray
+	Deposit       uint64
+	RewardAccount Address
+	GovAction     GovActionWrapper
+	Anchor        GovAnchor
+}
+
+const (
+	GovActionTypeParameterChange    = 0
+	GovActionTypeHardForkInitiation = 1
+	GovActionTypeTreasuryWithdrawal = 2
+	GovActionTypeNoConfidence       = 3
+	GovActionTypeUpdateCommittee    = 4
+	GovActionTypeNewConstitution    = 5
+	GovActionTypeInfo               = 6
+)
+
+type GovActionWrapper struct {
+	Type   uint
+	Action GovAction
+}
+
+func (g *GovActionWrapper) UnmarshalCBOR(data []byte) error {
+	// Determine action type
+	actionType, err := cbor.DecodeIdFromList(data)
+	if err != nil {
+		return err
+	}
+	var tmpAction GovAction
+	switch actionType {
+	case GovActionTypeParameterChange:
+		tmpAction = &ParameterChangeGovAction{}
+	case GovActionTypeHardForkInitiation:
+		tmpAction = &HardForkInitiationGovAction{}
+	case GovActionTypeTreasuryWithdrawal:
+		tmpAction = &TreasuryWithdrawalGovAction{}
+	case GovActionTypeNoConfidence:
+		tmpAction = &NoConfidenceGovAction{}
+	case GovActionTypeUpdateCommittee:
+		tmpAction = &UpdateCommitteeGovAction{}
+	case GovActionTypeNewConstitution:
+		tmpAction = &NewConstitutionGovAction{}
+	case GovActionTypeInfo:
+		tmpAction = &InfoGovAction{}
+	default:
+		return fmt.Errorf("unknown governance action type: %d", actionType)
+	}
+	// Decode action
+	if _, err := cbor.Decode(data, tmpAction); err != nil {
+		return err
+	}
+	g.Type = uint(actionType)
+	g.Action = tmpAction
+	return nil
+}
+
+func (g *GovActionWrapper) MarshalCBOR() ([]byte, error) {
+	return cbor.Encode(g.Action)
+}
+
+type GovAction interface {
+	isGovAction()
+}
+
+// parameter_change_action = (0, gov_action_id / null, protocol_param_update, policy_hash / null)
+type ParameterChangeGovAction struct {
+	cbor.StructAsArray
+	Type        uint
+	ActionId    *GovActionId
+	ParamUpdate BabbageProtocolParameterUpdate // TODO: use Conway params update type
+	PolicyHash  []byte
+}
+
+func (a ParameterChangeGovAction) isGovAction() {}
+
+// hard_fork_initiation_action = (1, gov_action_id / null, protocol_version)
+type HardForkInitiationGovAction struct {
+	cbor.StructAsArray
+	Type            uint
+	ActionId        *GovActionId
+	ProtocolVersion struct {
+		cbor.StructAsArray
+		Major uint
+		Minor uint
+	}
+}
+
+func (a HardForkInitiationGovAction) isGovAction() {}
+
+// treasury_withdrawals_action = (2, { reward_account => coin }, policy_hash / null)
+type TreasuryWithdrawalGovAction struct {
+	cbor.StructAsArray
+	Type        uint
+	Withdrawals map[*Address]uint64
+	PolicyHash  []byte
+}
+
+func (a TreasuryWithdrawalGovAction) isGovAction() {}
+
+// no_confidence = (3, gov_action_id / null)
+type NoConfidenceGovAction struct {
+	cbor.StructAsArray
+	Type     uint
+	ActionId *GovActionId
+}
+
+func (a NoConfidenceGovAction) isGovAction() {}
+
+// update_committee = (4, gov_action_id / null, set<committee_cold_credential>, { committee_cold_credential => epoch }, unit_interval)
+type UpdateCommitteeGovAction struct {
+	cbor.StructAsArray
+	Type        uint
+	ActionId    *GovActionId
+	Credentials []StakeCredential
+	CredEpochs  map[*StakeCredential]uint
+	Unknown     cbor.Rat
+}
+
+func (a UpdateCommitteeGovAction) isGovAction() {}
+
+/*
+new_constitution = (5, gov_action_id / null, constitution)
+
+constitution =
+
+	[ anchor
+	, scripthash / null
+	]
+*/
+type NewConstitutionGovAction struct {
+	cbor.StructAsArray
+	Type         uint
+	ActionId     *GovActionId
+	Constitution struct {
+		cbor.StructAsArray
+		Anchor     GovAnchor
+		ScriptHash []byte
+	}
+}
+
+func (a NewConstitutionGovAction) isGovAction() {}
+
+// info_action = 6
+type InfoGovAction struct {
+	cbor.StructAsArray
+	Type uint
+}
+
+func (a InfoGovAction) isGovAction() {}
+
 type ConwayTransaction struct {
 	cbor.StructAsArray
 	cbor.DecodeStoreCbor