fix gas loop optimization in MerkleProof.sol (OpenZeppelin#5028)

contracts/utils/cryptography/MerkleProof.sol

@@ -50,8 +50,11 @@ library MerkleProof {
      */
     function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
         bytes32 computedHash = leaf;
-        for (uint256 i = 0; i < proof.length; i++) {
+        for (uint256 i; i < proof.length; ) {
             computedHash = Hashes.commutativeKeccak256(computedHash, proof[i]);
+            unchecked {
+                ++i;
+            }
         }
         return computedHash;
     }
@@ -61,8 +64,11 @@ library MerkleProof {
      */
     function processProofCalldata(bytes32[] calldata proof, bytes32 leaf) internal pure returns (bytes32) {
         bytes32 computedHash = leaf;
-        for (uint256 i = 0; i < proof.length; i++) {
+        for (uint256 i; i < proof.length; ) {
             computedHash = Hashes.commutativeKeccak256(computedHash, proof[i]);
+            unchecked {
+                ++i;
+            }
         }
         return computedHash;
     }
@@ -135,12 +141,15 @@ library MerkleProof {
         //   get the next hash.
         // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
         //   `proof` array.
-        for (uint256 i = 0; i < totalHashes; i++) {
+        for (uint256 i; i < totalHashes; ) {
             bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
             bytes32 b = proofFlags[i]
                 ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                 : proof[proofPos++];
             hashes[i] = Hashes.commutativeKeccak256(a, b);
+            unchecked {
+                ++i;
+            }
         }
 
         if (totalHashes > 0) {
@@ -191,12 +200,15 @@ library MerkleProof {
         //   get the next hash.
         // - depending on the flag, either another value from the "main queue" (merging branches) or an element from the
         //   `proof` array.
-        for (uint256 i = 0; i < totalHashes; i++) {
+        for (uint256 i; i < totalHashes; ) {
             bytes32 a = leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++];
             bytes32 b = proofFlags[i]
                 ? (leafPos < leavesLen ? leaves[leafPos++] : hashes[hashPos++])
                 : proof[proofPos++];
             hashes[i] = Hashes.commutativeKeccak256(a, b);
+            unchecked {
+                ++i;
+            }
         }
 
         if (totalHashes > 0) {