core: tighten metric doc comments

- Replace reader.go:553 line citation in GetStateStats with the function
  name; line numbers rot.
- Note the BAL sum-of-CPU-time semantics on the read-time field group
  in ExecuteStats so cross-client consumers don't read total ≤ TotalTime
  as an invariant.

core/blockchain_stats.go

@@ -28,7 +28,9 @@ import (
 
 // ExecuteStats includes all the statistics of a block execution in details.
 type ExecuteStats struct {
-	// State read times
+	// State read times. For BAL blocks these are sum-of-CPU-time across
+	// per-tx, pre-tx, post-tx, BAL state-transition and prefetcher paths;
+	// can exceed TotalTime by design. Sequential blocks: wall-clock.
 	AccountReads   time.Duration // Time spent on the account reads
 	StorageReads   time.Duration // Time spent on the storage reads
 	AccountHashes  time.Duration // Time spent on the account trie hash

core/state/reader_eip_7928.go

@@ -375,8 +375,8 @@ func (r *readerTracker) TouchStorage(addr common.Address, slot common.Hash) {
 }
 
 // GetStateStats forwards stats from the wrapped *stateReaderWithStats so the
-// reader-aggregator type assertion at reader.go:553 succeeds. Without this,
-// account/storage cache hit/miss counts emit zero on BAL blocks.
+// (*reader).GetStateStats type assertion succeeds. Without this, account/
+// storage cache hit/miss counts emit zero on BAL blocks.
 func (r *prefetchStateReader) GetStateStats() StateReaderStats {
 	if stater, ok := r.StateReader.(StateReaderStater); ok {
 		return stater.GetStateStats()