Add unit tests for Vector3Serializer round-trip serialization

[xinzhoudev]

This PR introduces Vector3SerializerTest, a JUnit test class that validates the round-trip correctness of Vector3Serializer, which is responsible for encoding Vector3f positions and directions in multiplayer network messages.

[gemini-code-assist]

Code Review

This pull request introduces unit tests for the Vector3Serializer class, verifying that it correctly serializes and deserializes Vector3f objects. However, there is a package mismatch in the new test file where the declared package does not match its directory path, which will cause compilation errors. A suggestion has been provided to correct the package declaration and add the necessary import.

[gemini-code-assist]

The package declaration com.jme3.network.serializing.serializers does not match the file's directory path com/jme3/network/message/. This will cause compilation errors. Please update the package declaration to com.jme3.network.message and import Vector3Serializer explicitly.

Suggested change

	package com.jme3.network.serializing.serializers;
	import com.jme3.math.Vector3f;
	import java.io.IOException;
	import java.nio.ByteBuffer;
	import org.junit.Test;
	package com.jme3.network.message;
	import com.jme3.math.Vector3f;
	import com.jme3.network.serializing.serializers.Vector3Serializer;
	import java.io.IOException;
	import java.nio.ByteBuffer;
	import org.junit.Test;