Use memory-safe for the SafeMock Fallback Implementation (#200)

I noticed that the `fallback` function implementation was not memory
safe for the SafeMock contract. This PR rectifies this.

Additionally, FCL assembly is also not tagged as memory safe (but should
be AFAIU). We should probably submit a PR upstream to tag assembly as
memory safe.

4337/contracts/test/SafeMock.sol

@@ -71,22 +71,24 @@ contract SafeMock {
     // solhint-disable-next-line payable-fallback,no-complex-fallback
     fallback() external payable {
         // solhint-disable-next-line no-inline-assembly
-        assembly {
+        assembly ("memory-safe") {
             let handler := sload(fallbackHandler.slot)
             if iszero(handler) {
                 return(0, 0)
             }
-            calldatacopy(0, 0, calldatasize())
+
+            let ptr := mload(0x40)
+            calldatacopy(ptr, 0, calldatasize())
             // The msg.sender address is shifted to the left by 12 bytes to remove the padding
             // Then the address without padding is stored right after the calldata
-            mstore(calldatasize(), shl(96, caller()))
+            mstore(add(ptr, calldatasize()), shl(96, caller()))
             // Add 20 bytes for the address appended add the end
-            let success := call(gas(), handler, 0, 0, add(calldatasize(), 20), 0, 0)
-            returndatacopy(0, 0, returndatasize())
+            let success := call(gas(), handler, 0, ptr, add(calldatasize(), 20), 0, 0)
+            returndatacopy(ptr, 0, returndatasize())
             if iszero(success) {
-                revert(0, returndatasize())
+                revert(ptr, returndatasize())
             }
-            return(0, returndatasize())
+            return(ptr, returndatasize())
         }
     }