feat(contracts): add input relay interface and base contract

onchain/rollups/contracts/inputs/IInputRelay.sol

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+// Copyright Cartesi Pte. Ltd.
+
+// SPDX-License-Identifier: Apache-2.0
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+pragma solidity ^0.8.8;
+
+import {IInputBox} from "./IInputBox.sol";
+
+/// @title Input Relay interface
+interface IInputRelay {
+    // Permissionless functions
+
+    /// @notice Get the input box used by this input relay.
+    /// @return The input box
+    function getInputBox() external view returns (IInputBox);
+}

onchain/rollups/contracts/inputs/InputRelay.sol

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+// Copyright Cartesi Pte. Ltd.
+
+// SPDX-License-Identifier: Apache-2.0
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
+// this file except in compliance with the License. You may obtain a copy of the
+// License at http://www.apache.org/licenses/LICENSE-2.0
+
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations under the License.
+
+pragma solidity ^0.8.8;
+
+import {IInputRelay} from "./IInputRelay.sol";
+import {IInputBox} from "./IInputBox.sol";
+
+/// @title Input Relay
+/// @notice This contract serves as a base for all the other input relays.
+contract InputRelay is IInputRelay {
+    /// @notice The input box used by the input relay.
+    IInputBox internal immutable inputBox;
+
+    /// @notice Constructs the input relay.
+    /// @param _inputBox The input box used by the input relay
+    constructor(IInputBox _inputBox) {
+        inputBox = _inputBox;
+    }
+
+    function getInputBox() external view override returns (IInputBox) {
+        return inputBox;
+    }
+}