feat: Add swap method (first attempt)

Will add tests and fullproof it in a future PR

--- don't change below this line ---
ENG-4041 Took 8 minutes

Took 42 seconds

Took 5 seconds

foundry/src/Swap.sol

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.28;
+
+library Swap {
+    /// Returns the InToken index into an array of tokens
+    function tokenInIndex(bytes calldata swap)
+        internal
+        pure
+        returns (uint8 res)
+    {
+        res = uint8(swap[0]);
+    }
+
+    /// The OutToken index into an array of tokens
+    function tokenOutIndex(bytes calldata swap)
+        internal
+        pure
+        returns (uint8 res)
+    {
+        res = uint8(swap[1]);
+    }
+
+    /// The relative amount of token quantity routed into this swap
+    function splitPercentage(bytes calldata swap)
+        internal
+        pure
+        returns (uint24 res)
+    {
+        res = uint24(bytes3(swap[2:5]));
+    }
+
+    /// Remaining bytes are interpreted as protocol data
+    function protocolData(bytes calldata swap)
+        internal
+        pure
+        returns (bytes calldata res)
+    {
+        res = swap[5:];
+    }
+}