fix: use encodePacked to encode if approval needed

- Also approve max amount for the tycho router to use (to save on gas)

foundry/src/uniswap_x/UniswapXFiller.sol

@@ -67,17 +67,15 @@ contract UniswapXFiller is AccessControl, IReactorCallback {
 
         ResolvedOrder memory order = resolvedOrders[0];
 
-        (
-            bool tokenInApprovalNeeded,
-            bool tokenOutApprovalNeeded,
-            bytes memory tychoCalldata
-        ) = abi.decode(callbackData, (bool, bool, bytes));
+        bool tokenInApprovalNeeded = bool(uint8(callbackData[0]) == 1);
+        bool tokenOutApprovalNeeded = bool(uint8(callbackData[1]) == 1);
+        bytes calldata tychoCalldata = bytes(callbackData[2:]);
 
         // The TychoRouter will take the input tokens from the filler
         if (tokenInApprovalNeeded) {
             // Native ETH input is not supported by UniswapX
             IERC20(order.input.token).forceApprove(
-                tychoRouter, order.input.maxAmount
+                tychoRouter, type(uint256).max
             );
         }
 

foundry/test/uniswap_x/UniswapXFiller.t.sol

@@ -68,7 +68,8 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
             swap
         );
 
-        bytes memory callbackData = abi.encode(true, true, tychoRouterData);
+        bytes memory callbackData =
+            abi.encodePacked(true, true, tychoRouterData);
 
         deal(WETH_ADDR, address(filler), amountIn);
         vm.startPrank(address(filler));
@@ -153,7 +154,7 @@ contract UniswapXFillerTest is Test, TychoRouterTestSetup {
             swap
         );
 
-        bytes memory callbackData = abi.encode(
+        bytes memory callbackData = abi.encodePacked(
             true, // tokenIn approval needed
             true, // tokenOut approval needed
             tychoRouterData