perf(state): Cache the block hash (backport cometbft#2924) (cometbft#…

…2931)

Closes cometbft#2923 

Caches the block hash to ensure we only compute it once in consensus
execution.

---

#### PR checklist

- [x] Tests written/updated - not sure what test I should write, any
suggestions?
- [x] Changelog entry added in `.changelog` (we use
[unclog](https://github.com/informalsystems/unclog) to manage our
changelog)
- [ ] Updated relevant documentation (`docs/` or `spec/`) and code
comments
- [x] Title follows the [Conventional
Commits](https://www.conventionalcommits.org/en/v1.0.0/) spec
<hr>This is an automatic backport of pull request cometbft#2924 done by
[Mergify](https://mergify.com).

Co-authored-by: Dev Ojha <[email protected]>

.changelog/unreleased/improvements/2924-consensus-cache-block-hash.md

@@ -0,0 +1,2 @@
+- `[state/execution]` Cache the block hash computation inside of the Block Type, so we only compute it once.
+  ([\#2924](https://github.com/cometbft/cometbft/pull/2924))

types/block.go

@@ -43,10 +43,11 @@ const (
 type Block struct {
 	mtx cmtsync.Mutex
 
-	Header     `json:"header"`
-	Data       `json:"data"`
-	Evidence   EvidenceData `json:"evidence"`
-	LastCommit *Commit      `json:"last_commit"`
+	verifiedHash cmtbytes.HexBytes // Verified block hash (not included in the struct hash)
+	Header       `json:"header"`
+	Data         `json:"data"`
+	Evidence     EvidenceData `json:"evidence"`
+	LastCommit   *Commit      `json:"last_commit"`
 }
 
 // ValidateBasic performs basic validation that doesn't involve state data.
@@ -130,8 +131,13 @@ func (b *Block) Hash() cmtbytes.HexBytes {
 	if b.LastCommit == nil {
 		return nil
 	}
+	if b.verifiedHash != nil {
+		return b.verifiedHash
+	}
 	b.fillHeader()
-	return b.Header.Hash()
+	hash := b.Header.Hash()
+	b.verifiedHash = hash
+	return hash
 }
 
 // MakePartSet returns a PartSet containing parts of a serialized block.