feat: add getMappings method for unmodifiable view of particle mappings

Add a public static method `getMappings()` that returns an unmodifiable
view of the internal mappings map. This provides safe read-only access
to the particle mappings for external consumers while preventing
accidental modifications.

Author: GeorgeV220

src/main/java/com/georgev22/particle/ParticleMappings.java

@@ -3,12 +3,16 @@
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonParser;
+import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.UnmodifiableView;
+import org.jspecify.annotations.NonNull;
 
 import java.io.InputStreamReader;
 import java.lang.reflect.Field;
 import java.lang.reflect.Method;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Objects;
@@ -157,4 +161,14 @@ public static Field getMappedField(Class<?> targetClass, String name, boolean de
         if (mapped == null) return null;
         return getFieldOrNull(targetClass, mapped, declared);
     }
+
+    /**
+     * Gets an unmodifiable view of the mappings.
+     *
+     * @return an unmodifiable view of the mappings
+     */
+    @Contract(pure = true)
+    public static @NonNull @UnmodifiableView Map<String, String> getMappings() {
+        return Collections.unmodifiableMap(mappings);
+    }
 }