wire, btcutil, main: Use DoubleHashRaw for TxHash and WitnessHash

DoubleHashRaw is able to save on the allocation made by the msgtx
serialization by directly serializing onto the sha256 digest.  This
results in massive amounts of memory savings in allocations during the
initial block download.

btcutil/go.mod

@@ -14,3 +14,5 @@ require (
 )
 
 replace github.com/btcsuite/btcd => ../
+
+replace github.com/btcsuite/btcd/chaincfg/chainhash => ../chaincfg/chainhash

btcutil/psbt/go.mod

@@ -24,3 +24,5 @@ require (
 replace github.com/btcsuite/btcd/btcutil => ../
 
 replace github.com/btcsuite/btcd => ../..
+
+replace github.com/btcsuite/btcd/chaincfg/chainhash => ../../chaincfg/chainhash

go.mod

@@ -31,6 +31,8 @@ require (
 
 replace github.com/btcsuite/btcd/btcutil => ./btcutil
 
+replace github.com/btcsuite/btcd/chaincfg/chainhash => ./chaincfg/chainhash
+
 // The retract statements below fixes an accidental push of the tags of a btcd
 // fork.
 retract (
@@ -63,4 +65,4 @@ retract (
 	v0.13.0-beta
 )
 
-go 1.17
+go 1.18

wire/msgtx.go

@@ -5,7 +5,6 @@
 package wire
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"io"
@@ -357,13 +356,7 @@ func (msg *MsgTx) AddTxOut(to *TxOut) {
 
 // TxHash generates the Hash for the transaction.
 func (msg *MsgTx) TxHash() chainhash.Hash {
-	// Encode the transaction and calculate double sha256 on the result.
-	// Ignore the error returns since the only way the encode could fail
-	// is being out of memory or due to nil pointers, both of which would
-	// cause a run-time panic.
-	buf := bytes.NewBuffer(make([]byte, 0, msg.SerializeSizeStripped()))
-	_ = msg.SerializeNoWitness(buf)
-	return chainhash.DoubleHashH(buf.Bytes())
+	return chainhash.DoubleHashRaw(msg.SerializeNoWitness)
 }
 
 // WitnessHash generates the hash of the transaction serialized according to
@@ -373,9 +366,7 @@ func (msg *MsgTx) TxHash() chainhash.Hash {
 // is the same as its txid.
 func (msg *MsgTx) WitnessHash() chainhash.Hash {
 	if msg.HasWitness() {
-		buf := bytes.NewBuffer(make([]byte, 0, msg.SerializeSize()))
-		_ = msg.Serialize(buf)
-		return chainhash.DoubleHashH(buf.Bytes())
+		return chainhash.DoubleHashRaw(msg.Serialize)
 	}
 
 	return msg.TxHash()