Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/ArraysMock.sol

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../utils/Arrays.sol";
+
+contract Uint256ArraysMock {
+    using Arrays for uint256[];
+
+    uint256[] private _array;
+
+    constructor(uint256[] memory array) {
+        _array = array;
+    }
+
+    function findUpperBound(uint256 element) external view returns (uint256) {
+        return _array.findUpperBound(element);
+    }
+
+    function unsafeAccess(uint256 pos) external view returns (uint256) {
+        return _array.unsafeAccess(pos).value;
+    }
+}
+
+contract AddressArraysMock {
+    using Arrays for address[];
+
+    address[] private _array;
+
+    constructor(address[] memory array) {
+        _array = array;
+    }
+
+    function unsafeAccess(uint256 pos) external view returns (address) {
+        return _array.unsafeAccess(pos).value;
+    }
+}
+
+contract Bytes32ArraysMock {
+    using Arrays for bytes32[];
+
+    bytes32[] private _array;
+
+    constructor(bytes32[] memory array) {
+        _array = array;
+    }
+
+    function unsafeAccess(uint256 pos) external view returns (bytes32) {
+        return _array.unsafeAccess(pos).value;
+    }
+}