✨ introduce account v2 draft code

This draft boilerplate introduces the upgrade function that reinitializes
the contract and burns the nonce 0. The burn of the nonce 0 is required
if the entrypoint changes. There are no consequences for burning arbitrary
nonce value

src/v2/Account/SmartAccount.sol

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: Apache-2.0
+pragma solidity >=0.8.20 <0.9.0;
+
+import { SmartAccount as SmartAccountV1 } from "src/v1/Account/SmartAccount.sol";
+import { IEntryPoint } from "@eth-infinitism/interfaces/IEntryPoint.sol";
+
+/// @custom:experimental This is just a draft of the new version of the SmartAccount contract.
+///                      The most important part here is the behavior of the `upgrade` function.
+contract SmartAccount is SmartAccountV1 {
+    constructor(address entryPoint, address webAuthnVerifier) SmartAccountV1(entryPoint, webAuthnVerifier) { }
+
+    function upgrade() external virtual reinitializer(2) {
+        // burn the nonce 0 -- this will prevent the creation flow from being called again
+        IEntryPoint(entryPointAddress).incrementNonce(0);
+    }
+}