asset+proof: add block timestamp to ChainAsset

This adds a new `AnchorBlockTimestamp` field to the `ChainAsset` struct
which gets set to the timestamp of the block header encoded in the
`Proof`.

Author: jamaljsr

asset/asset.go

@@ -1863,6 +1863,10 @@ type ChainAsset struct {
 	// tx.
 	AnchorBlockHeight uint32
 
+	// AnchorBlockTimestamp is the Unix timestamp of the block that mined
+	// the anchor tx.
+	AnchorBlockTimestamp int64
+
 	// AnchorOutpoint is the outpoint that commits to the asset.
 	AnchorOutpoint wire.OutPoint
 

proof/proof.go

@@ -530,6 +530,7 @@ func (p *Proof) ToChainAsset() (asset.ChainAsset, error) {
 		AnchorBlockHash:        p.BlockHeader.BlockHash(),
 		AnchorOutpoint:         p.OutPoint(),
 		AnchorBlockHeight:      p.BlockHeight,
+		AnchorBlockTimestamp:   p.BlockHeader.Timestamp.Unix(),
 		AnchorInternalKey:      p.InclusionProof.InternalKey,
 		AnchorMerkleRoot:       merkleRoot[:],
 		AnchorTapscriptSibling: tsSibling,