Nomad changes

docs/snippets/java/plugins/stateful_plugin.md

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+```java title="Java"
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+class StatefulPlugin implements PostProcessor {
+    // Use atomic types for simple counters
+    private final AtomicInteger callCount = new AtomicInteger(0);
+
+    // Use concurrent collections for complex state
+    private final ConcurrentHashMap<String, String> cache = new ConcurrentHashMap<>();
+
+    @Override
+    public ExtractionResult process(ExtractionResult result) {
+        // Increment counter atomically
+        callCount.incrementAndGet();
+
+        // Update cache (thread-safe)
+        cache.put("last_mime", result.mimeType());
+
+        return result;
+    }
+
+    public int getCallCount() {
+        return callCount.get();
+    }
+}
+```