fix: Address Copilot review comments

- Make server availability probe static/one-time in ResetTest (avoids
  redundant client+query per test method)
- Use CopyOnWriteArrayList in concurrent reset+query test for thread safety
- Add closed guard in queryWithParams() for consistent IllegalStateException
  instead of confusing NPE after close()

Author: phillipleblanc

src/main/java/ai/spice/SpiceClient.java

@@ -509,6 +509,9 @@ public ArrowReader queryWithParams(String sql, Object... params) throws Executio
         if (Strings.isNullOrEmpty(sql)) {
             throw new IllegalArgumentException("No SQL query provided");
         }
+        if (closed) {
+            throw new IllegalStateException("Cannot query with a closed SpiceClient");
+        }
 
         logger.debug("Executing parameterized query with {} parameters: {}", params != null ? params.length : 0, sql);
         try {

src/test/java/ai/spice/ResetTest.java

@@ -23,8 +23,8 @@ of this software and associated documentation files (the "Software"), to deal
 package ai.spice;
 
 import java.net.URI;
-import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
@@ -42,18 +42,27 @@ of this software and associated documentation files (the "Software"), to deal
  */
 public class ResetTest extends TestCase {
 
-    private boolean serverAvailable = false;
+    private static volatile boolean serverAvailable = false;
+    private static volatile boolean serverAvailabilityChecked = false;
 
     @Override
     protected void setUp() throws Exception {
         super.setUp();
-        try (SpiceClient probe = SpiceClient.builder().build()) {
-            try (FlightStream stream = probe.query("SELECT 1")) {
-                stream.next();
+        if (!serverAvailabilityChecked) {
+            synchronized (ResetTest.class) {
+                if (!serverAvailabilityChecked) {
+                    try (SpiceClient probe = SpiceClient.builder().build()) {
+                        try (FlightStream stream = probe.query("SELECT 1")) {
+                            stream.next();
+                        }
+                        serverAvailable = true;
+                    } catch (Exception e) {
+                        serverAvailable = false;
+                    } finally {
+                        serverAvailabilityChecked = true;
+                    }
+                }
             }
-            serverAvailable = true;
-        } catch (Exception e) {
-            serverAvailable = false;
         }
     }
 
@@ -257,7 +266,7 @@ public void testConcurrentResetAndQuery() throws Exception {
         final SpiceClient client = SpiceClient.builder().build();
         final int iterations = 5;
         final CountDownLatch startLatch = new CountDownLatch(1);
-        final List<Throwable> unexpectedErrors = new ArrayList<>();
+        final List<Throwable> unexpectedErrors = new CopyOnWriteArrayList<>();
         ExecutorService executor = Executors.newFixedThreadPool(2);
 
         try {