fix(net): avoid panics on malformed encryption/velocity login responses (#2310)

`handle_encryption_response` unwrapped the RSA decrypt of the
client-supplied shared secret, panicking the connection task on a
malformed value; kick the client instead, mirroring the adjacent
`set_encryption` error handling.

`receive_velocity_plugin_response` called `data.split_at(32)` without a
length check, panicking on a velocity response shorter than 32 bytes;
guard the length and return `FailedVerifyIntegrity`.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pumpkin/src/net/java/login.rs

@@ -114,10 +114,11 @@ impl JavaClient {
         encryption_response: SEncryptionResponse,
     ) {
         debug!("Handling encryption");
-        let shared_secret = server
-            .decrypt(&encryption_response.shared_secret)
-            .await
-            .unwrap();
+        let Ok(shared_secret) = server.decrypt(&encryption_response.shared_secret).await else {
+            self.kick(TextComponent::text("Failed to decrypt shared secret"))
+                .await;
+            return;
+        };
 
         if let Err(error) = self.set_encryption(&shared_secret).await {
             self.kick(TextComponent::text(error.to_string())).await;

pumpkin/src/net/proxy/velocity.rs

@@ -112,6 +112,9 @@ pub fn receive_velocity_plugin_response(
 ) -> Result<(GameProfile, SocketAddr), VelocityError> {
     debug!("Received velocity response");
     if let Some(data) = response.data {
+        if data.len() < 32 {
+            return Err(VelocityError::FailedVerifyIntegrity);
+        }
         let (signature, mut data_without_signature) = data.split_at(32);
 
         if !check_integrity((signature, data_without_signature), &config.secret) {