fix: lthash worker loop break; remove unreachable digest.Read fallback (#2698)

## Describe your changes and provide context

- Since `start := w * chunkSize` is monotonic, we switched both loops
from continue to break to avoid unnecessary iterations.
- remove unreachable digest.Read fallback
 
## Testing performed to validate your change

Author: blindchaser

sei-db/state_db/sc/flatkv/lthash/api.go

@@ -99,7 +99,7 @@ func computeDelta(kvPairs []KVPairWithLastValue, numWorkers int) (*LtHash, *LtHa
 	for w := 0; w < numWorkers; w++ {
 		start := w * chunkSize
 		if start >= len(kvPairs) {
-			continue
+			break
 		}
 		end := start + chunkSize
 		if end > len(kvPairs) {
@@ -130,7 +130,7 @@ func computeDelta(kvPairs []KVPairWithLastValue, numWorkers int) (*LtHash, *LtHa
 	for w := 0; w < numWorkers; w++ {
 		start := w * chunkSize
 		if start >= len(kvPairs) {
-			continue
+			break
 		}
 		end := start + chunkSize
 		if end > len(kvPairs) {

sei-db/state_db/sc/flatkv/lthash/lthash.go

@@ -137,21 +137,9 @@ func hash(data []byte) *LtHash {
 
 	bufPtr := xofBufferPool.Get().(*[]byte)
 	output := *bufPtr
-	n, err := digest.Read(output)
+	_, _ = digest.Read(output) // Blake3 XOF never errors and always fills buffer
 	blake3HasherPool.Put(hasher)
 
-	if err != nil || n != LtHashBytes {
-		xofBufferPool.Put(bufPtr)
-		h := blake3.Sum256(data)
-		output = extendTo2048Bytes(h[:])
-
-		lth := ltHashPool.Get().(*LtHash)
-		for i := 0; i < LtHashSize; i++ {
-			lth.limbs[i] = binary.LittleEndian.Uint16(output[i*2:])
-		}
-		return lth
-	}
-
 	lth := ltHashPool.Get().(*LtHash)
 	for i := 0; i < LtHashSize; i++ {
 		lth.limbs[i] = binary.LittleEndian.Uint16(output[i*2 : (i+1)*2])
@@ -224,18 +212,3 @@ func putLtHashToPool(lth *LtHash) {
 		ltHashPool.Put(lth)
 	}
 }
-
-func extendTo2048Bytes(seed []byte) []byte {
-	result := make([]byte, LtHashBytes)
-	copy(result[:32], seed)
-	for i := 32; i < LtHashBytes; i += 32 {
-		chunk := result[i-32 : i]
-		h := blake3.Sum256(chunk)
-		copy(result[i:], h[:])
-		if i+32 > LtHashBytes {
-			copy(result[i:], h[:LtHashBytes-i])
-			break
-		}
-	}
-	return result
-}