refactor(samples): Add Future import and async library comment (EME-413)

Improves code readability by importing Future instead of using fully qualified name.
Adds guidance comment suggesting developers convert the sample to their preferred
async library (RxJava, Coroutines, etc.) in production code.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: runningcode

sentry-samples/sentry-samples-android/src/main/java/io/sentry/samples/android/MainActivity.java

@@ -29,6 +29,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Future;
 import timber.log.Timber;
 
 public class MainActivity extends AppCompatActivity {
@@ -315,7 +316,9 @@ public void run() {
     binding.checkForUpdate.setOnClickListener(
         view -> {
           Toast.makeText(this, "Checking for updates...", Toast.LENGTH_SHORT).show();
-          java.util.concurrent.Future<UpdateStatus> future = Sentry.distribution().checkForUpdate();
+          Future<UpdateStatus> future = Sentry.distribution().checkForUpdate();
+          // In production, convert this to use your preferred async library (RxJava, Coroutines, etc.)
+          // This sample uses raw threads and Future.get() for simplicity
           // Process result on background thread, then update UI
           new Thread(
                   () -> {