Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol

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+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.7.0) (crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol)
+
+pragma solidity ^0.8.4;
+
+import "../CrossChainEnabled.sol";
+import "./LibArbitrumL1.sol";
+
+/**
+ * @dev https://arbitrum.io/[Arbitrum] specialization or the
+ * {CrossChainEnabled} abstraction the L1 side (mainnet).
+ *
+ * This version should only be deployed on L1 to process cross-chain messages
+ * originating from L2. For the other side, use {CrossChainEnabledArbitrumL2}.
+ *
+ * The bridge contract is provided and maintained by the arbitrum team. You can
+ * find the address of this contract on the rinkeby testnet in
+ * https://developer.offchainlabs.com/docs/useful_addresses[Arbitrum's developer documentation].
+ *
+ * _Available since v4.6._
+ */
+abstract contract CrossChainEnabledArbitrumL1 is CrossChainEnabled {
+    /// @custom:oz-upgrades-unsafe-allow state-variable-immutable
+    address private immutable _bridge;
+
+    /// @custom:oz-upgrades-unsafe-allow constructor
+    constructor(address bridge) {
+        _bridge = bridge;
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_isCrossChain}
+     */
+    function _isCrossChain() internal view virtual override returns (bool) {
+        return LibArbitrumL1.isCrossChain(_bridge);
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_crossChainSender}
+     */
+    function _crossChainSender() internal view virtual override onlyCrossChain returns (address) {
+        return LibArbitrumL1.crossChainSender(_bridge);
+    }
+}

backend/lib/openzeppelin-contracts/contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol

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+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.8.0) (crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol)
+
+pragma solidity ^0.8.4;
+
+import "../CrossChainEnabled.sol";
+import "./LibArbitrumL2.sol";
+
+/**
+ * @dev https://arbitrum.io/[Arbitrum] specialization or the
+ * {CrossChainEnabled} abstraction the L2 side (arbitrum).
+ *
+ * This version should only be deployed on L2 to process cross-chain messages
+ * originating from L1. For the other side, use {CrossChainEnabledArbitrumL1}.
+ *
+ * Arbitrum L2 includes the `ArbSys` contract at a fixed address. Therefore,
+ * this specialization of {CrossChainEnabled} does not include a constructor.
+ *
+ * _Available since v4.6._
+ *
+ * WARNING: There is currently a bug in Arbitrum that causes this contract to
+ * fail to detect cross-chain calls when deployed behind a proxy. This will be
+ * fixed when the network is upgraded to Arbitrum Nitro, currently scheduled for
+ * August 31st 2022.
+ */
+abstract contract CrossChainEnabledArbitrumL2 is CrossChainEnabled {
+    /**
+     * @dev see {CrossChainEnabled-_isCrossChain}
+     */
+    function _isCrossChain() internal view virtual override returns (bool) {
+        return LibArbitrumL2.isCrossChain(LibArbitrumL2.ARBSYS);
+    }
+
+    /**
+     * @dev see {CrossChainEnabled-_crossChainSender}
+     */
+    function _crossChainSender() internal view virtual override onlyCrossChain returns (address) {
+        return LibArbitrumL2.crossChainSender(LibArbitrumL2.ARBSYS);
+    }
+}

backend/lib/openzeppelin-contracts/contracts/crosschain/arbitrum/LibArbitrumL1.sol

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+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.8.0) (crosschain/arbitrum/LibArbitrumL1.sol)
+
+pragma solidity ^0.8.4;
+
+import {IBridge as ArbitrumL1_Bridge} from "../../vendor/arbitrum/IBridge.sol";
+import {IOutbox as ArbitrumL1_Outbox} from "../../vendor/arbitrum/IOutbox.sol";
+import "../errors.sol";
+
+/**
+ * @dev Primitives for cross-chain aware contracts for
+ * https://arbitrum.io/[Arbitrum].
+ *
+ * This version should only be used on L1 to process cross-chain messages
+ * originating from L2. For the other side, use {LibArbitrumL2}.
+ */
+library LibArbitrumL1 {
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message relayed by the `bridge`.
+     */
+    function isCrossChain(address bridge) internal view returns (bool) {
+        return msg.sender == bridge;
+    }
+
+    /**
+     * @dev Returns the address of the sender that triggered the current
+     * cross-chain message through the `bridge`.
+     *
+     * NOTE: {isCrossChain} should be checked before trying to recover the
+     * sender, as it will revert with `NotCrossChainCall` if the current
+     * function call is not the result of a cross-chain message.
+     */
+    function crossChainSender(address bridge) internal view returns (address) {
+        if (!isCrossChain(bridge)) revert NotCrossChainCall();
+
+        address sender = ArbitrumL1_Outbox(ArbitrumL1_Bridge(bridge).activeOutbox()).l2ToL1Sender();
+        require(sender != address(0), "LibArbitrumL1: system messages without sender");
+
+        return sender;
+    }
+}

backend/lib/openzeppelin-contracts/contracts/crosschain/arbitrum/LibArbitrumL2.sol

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+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.8.0) (crosschain/arbitrum/LibArbitrumL2.sol)
+
+pragma solidity ^0.8.4;
+
+import {IArbSys as ArbitrumL2_Bridge} from "../../vendor/arbitrum/IArbSys.sol";
+import "../errors.sol";
+
+/**
+ * @dev Primitives for cross-chain aware contracts for
+ * https://arbitrum.io/[Arbitrum].
+ *
+ * This version should only be used on L2 to process cross-chain messages
+ * originating from L1. For the other side, use {LibArbitrumL1}.
+ *
+ * WARNING: There is currently a bug in Arbitrum that causes this contract to
+ * fail to detect cross-chain calls when deployed behind a proxy. This will be
+ * fixed when the network is upgraded to Arbitrum Nitro, currently scheduled for
+ * August 31st 2022.
+ */
+library LibArbitrumL2 {
+    /**
+     * @dev Returns whether the current function call is the result of a
+     * cross-chain message relayed by `arbsys`.
+     */
+    address public constant ARBSYS = 0x0000000000000000000000000000000000000064;
+
+    function isCrossChain(address arbsys) internal view returns (bool) {
+        return ArbitrumL2_Bridge(arbsys).wasMyCallersAddressAliased();
+    }
+
+    /**
+     * @dev Returns the address of the sender that triggered the current
+     * cross-chain message through `arbsys`.
+     *
+     * NOTE: {isCrossChain} should be checked before trying to recover the
+     * sender, as it will revert with `NotCrossChainCall` if the current
+     * function call is not the result of a cross-chain message.
+     */
+    function crossChainSender(address arbsys) internal view returns (address) {
+        if (!isCrossChain(arbsys)) revert NotCrossChainCall();
+
+        return ArbitrumL2_Bridge(arbsys).myCallersAddressWithoutAliasing();
+    }
+}