feat: add LibPrefixLengthEncodedByteArray with tests

foundry/src/lib/LibPrefixLengthEncodedByteArray.sol

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.0;
+
+error LibPrefixLengthEncodedByteArray__InvalidEncoding();
+
+library LibPrefixLengthEncodedByteArray {
+    /**
+     * @dev Pop the first element of an array and returns it with the remaining data.
+     */
+    function next(bytes calldata encoded)
+        internal
+        pure
+        returns (bytes calldata elem, bytes calldata res)
+    {
+        // Handle empty input
+        if (encoded.length == 0) {
+            return (encoded[:0], encoded[:0]);
+        }
+
+        // Ensure we have at least 2 bytes for length prefix
+        if (encoded.length < 2) revert LibPrefixLengthEncodedByteArray__InvalidEncoding();
+        // Extract the length prefix (first 2 bytes)
+        uint16 length = uint16(bytes2(encoded[:2]));
+        
+        // Check if length is valid
+        if (2 + length > encoded.length) revert LibPrefixLengthEncodedByteArray__InvalidEncoding();
+        
+        // Extract the element (after length prefix)
+        elem = encoded[2:2+length];
+        
+        // Extract the remaining data
+        res = encoded[2+length:];
+        
+        return (elem, res);
+    }
+
+    /**
+     * @dev Gets the size of the encoded array.
+     */
+    function size(bytes calldata encoded) internal pure returns (uint256 s) {
+        uint256 offset = 0;
+
+        while (offset < encoded.length) {
+            // Ensure we have at least 2 bytes for length prefix
+            if (offset + 2 > encoded.length) revert LibPrefixLengthEncodedByteArray__InvalidEncoding();
+            
+            uint16 length = uint16(bytes2(encoded[offset:offset + 2]));
+            
+            // Check if length is valid
+            if (offset + 2 + length > encoded.length) revert LibPrefixLengthEncodedByteArray__InvalidEncoding();
+            
+            offset += length + 2;
+            s++;
+        }
+    }
+
+    /**
+     * @dev Cast an encoded array into a Solidity array.
+     */
+    function toArray(bytes calldata encoded)
+        internal
+        pure
+        returns (bytes[] memory arr)
+    {
+        bytes calldata elem;
+        uint256 idx = 0;
+        arr = new bytes[](LibPrefixLengthEncodedByteArray.size(encoded));
+        while (encoded.length > 0) {
+            (elem, encoded) = LibPrefixLengthEncodedByteArray.next(encoded);
+            arr[idx] = elem;
+            idx++;
+        }
+    }
+}