fix: external

Author: anna-carroll

src/Orders.sol

@@ -42,7 +42,7 @@ abstract contract OrderDestination {
     /// @param token - The address of the token to be transferred to the recipient.
     ///                address(0) corresponds to native Ether.
     /// @param amount - The amount of the token to be transferred to the recipient.
-    function fill(address recipient, address token, uint256 amount) public payable {
+    function fill(address recipient, address token, uint256 amount) external payable {
         if (token == address(0)) {
             require(amount == msg.value);
             payable(recipient).transfer(msg.value);