Add forced transaction inclusion interface (#151)

Author: DefiCake

.changeset/honest-dryers-promise.md

@@ -0,0 +1,5 @@
+---
+'@fuel-bridge/solidity-contracts': patch
+---
+
+Add FTI interface

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

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+// 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 Transaction(uint64 max_gas, bytes canonically_serialized_tx);
+
+    function sendTransaction(uint64 gas, bytes calldata serializedTx) external payable virtual;
+
+    function getLastSeenBlock() external virtual returns (uint256);
+
+    function getUsedGas() external virtual returns (uint64);
+}