core/state: change StateCounts.Add to value receiver

The struct is 80 bytes (10 ints) — value semantics matches the type's
"snapshot, safe to pass by value" thesis stated in its doc comment, and
removes three unnecessary &-takings at call sites. No behavior change.

core/blockchain.go

@@ -657,7 +657,7 @@ func (bc *BlockChain) processBlockWithAccessList(parentRoot common.Hash, block *
 	// (account/code/storage write counters via stateTransition.WriteCounts).
 	stats.StateCounts = res.Counts
 	balWrites := stateTransition.WriteCounts()
-	stats.StateCounts.Add(&balWrites)
+	stats.StateCounts.Add(balWrites)
 
 	// Time durations under parallel execution use wall-clock semantics.
 	// Per-tx duration sums (CPU-time) are intentionally not plumbed: they

core/blockchain_stats_test.go

@@ -53,7 +53,7 @@ func TestStateCountsAdd(t *testing.T) {
 		CodeUpdated:     900,
 		CodeUpdateBytes: 1000,
 	}
-	a.Add(&b)
+	a.Add(b)
 	want := state.StateCounts{
 		AccountLoaded:   101,
 		AccountUpdated:  202,

core/parallel_state_processor.go

@@ -183,7 +183,7 @@ func (p *ParallelStateProcessor) prepareExecResult(block *types.Block, tExecStar
 	// would otherwise be discarded; this captures system-contract reads and
 	// the engine.Finalize state mutations.
 	postTxCounts := postTxState.SnapshotCounts()
-	aggCounts.Add(&postTxCounts)
+	aggCounts.Add(postTxCounts)
 
 	// Fold post-tx statedb reads into the aggregate (system contracts,
 	// withdrawal queue, consolidation queue).
@@ -267,7 +267,7 @@ func (p *ParallelStateProcessor) resultHandler(block *types.Block, preTxReads ba
 						cumulativeStateGas += res.txState
 						results = append(results, res)
 						accesses.Merge(res.stateReads)
-						aggCounts.Add(&res.counts)
+						aggCounts.Add(res.counts)
 						aggAccountReads += res.accountReads
 						aggStorageReads += res.storageReads
 						aggCodeReads += res.codeReads

core/state/state_counts.go

@@ -43,9 +43,10 @@ type StateCounts struct {
 }
 
 // Add merges other into c. Plain integer addition — no atomics here, since
-// StateCounts is the snapshot type. Callers must ensure other is no longer
-// being mutated when Add is invoked.
-func (c *StateCounts) Add(other *StateCounts) {
+// StateCounts is the snapshot type. The receiver is the only mutated party;
+// other is taken by value (the struct is small and value semantics matches
+// the snapshot thesis stated above).
+func (c *StateCounts) Add(other StateCounts) {
 	c.AccountLoaded += other.AccountLoaded
 	c.AccountUpdated += other.AccountUpdated
 	c.AccountDeleted += other.AccountDeleted