fix: add PublicKey import back to test module

- Add PublicKey to test module imports to fix compilation errors
- test_guardian_address1() and test_guardian_address2() require PublicKey::from_secret_key()
- Resolves error[E0433]: failed to resolve: use of undeclared type 'PublicKey'

Co-Authored-By: ayush.suresh@dourolabs.xyz <byteSlayer31037@gmail.com>

target_chains/stylus/contracts/wormhole/src/lib.rs

@@ -538,7 +538,7 @@ mod tests {
     use alloc::vec;
     use motsu::prelude::DefaultStorage;
     use core::str::FromStr;
-    use libsecp256k1::{sign, Message, SecretKey};
+    use libsecp256k1::{sign, Message, SecretKey, PublicKey};
     use stylus_sdk::alloy_primitives::keccak256;
     use base64::engine::general_purpose;
     use base64::Engine;