add mock router snap

Author: snreynolds

snapshots/V4RouterTest.json

@@ -22,5 +22,6 @@
   "V4Router_ExactOut3Hops_nativeOut": "224943",
   "V4Router_ExactOutputSingle": "133337",
   "V4Router_ExactOutputSingle_nativeIn_sweepETH": "126419",
-  "V4Router_ExactOutputSingle_nativeOut": "119821"
+  "V4Router_ExactOutputSingle_nativeOut": "119821",
+  "position manager initcode hash (without constructor params, as uint256)": "27545762869727400677117557485685740862616789454191614676777323590122002226479"
 }

test/router/V4Router.gas.t.sol

@@ -22,6 +22,13 @@ contract V4RouterTest is RoutingTestHelpers {
         vm.snapshotValue("V4Router_Bytecode", address(router).code.length);
     }
 
+    function test_router_initcodeHash() public {
+        vm.snapshotValue(
+            "position manager initcode hash (without constructor params, as uint256)",
+            uint256(keccak256(abi.encodePacked(vm.getCode("MockV4Router.sol:MockV4Router"))))
+        );
+    }
+
     /*//////////////////////////////////////////////////////////////
                         ERC20 -> ERC20 EXACT INPUT
     //////////////////////////////////////////////////////////////*/