feat: add forced tx inclusion interface

Author: DefiCake

packages/solidity-contracts/contracts/fuelchain/FuelMessagePortal/IFuelMessagePortal.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: Apache 2.0
+pragma solidity 0.8.9;
+
+import {FuelMessagePortalV3} from "./v3/FuelMessagePortalV3.sol";
+
+/// @notice to be used by external tools, like the block producer
+/// @dev marked abstract to track all relevant current and future functions as development evolves
+abstract contract IFuelMessagePortal is FuelMessagePortalV3 {
+    event TransactionSent(bytes serializedTx, uint64);
+
+    function sendTransaction(bytes calldata serializedTx, uint64 gas) external payable virtual;
+
+    function getLastSeenBlock() external virtual returns (uint256);
+
+    function getUsedGas() external virtual returns (uint64);
+}