[FLINK-AGENTS][api] Fix Kryo deserialization failure for Event classes with immutable lists

[avichaym]

fixes #673

Wraps list arguments in new ArrayList<>() before passing to setAttr() in ChatRequestEvent, ContextRetrievalResponseEvent, and ToolRequestEvent. Without this, passing List.of(...) crashes Kryo on JDK 17+ with InaccessibleObjectException.

[wenjin272]

Hi, @avichaym, Ty for this fix.

The current fix looks good to me, but I think two additional points need to be added:

1. If user use Map.of to consturct ToolResponseEvent, there will likely be issues as well.
2. Supplement with relevant tests. Since in the CI pipeline, the test cases in flink-agents-end-to-end-tests-integration module will be executed in jdk 17 with flink 1.20, 2.0, 2.1 and 2.2. I think we can add a EventKryoSerializationTest in this module like:

@Test
void chatRequestEventWithImmutableListSurvivesKryoRoundTrip() throws Exception {
    ChatRequestEvent event =
            new ChatRequestEvent(
                    "myModel", List.of(new ChatMessage(MessageRole.USER, "hello")));

    ChatRequestEvent roundTripped = roundTrip(event, ChatRequestEvent.class);

    assertEquals("myModel", roundTripped.getModel());
    assertNotNull(roundTripped.getMessages());
    assertEquals(1, roundTripped.getMessages().size());
    assertEquals("hello", roundTripped.getMessages().get(0).getContent());
}
private static <T extends Event> T roundTrip(T event, Class<T> cls) throws Exception {
    KryoSerializer<T> serializer = new KryoSerializer<>(cls, new SerializerConfigImpl());
    DataOutputSerializer out = new DataOutputSerializer(64);
    serializer.serialize(event, out);
    DataInputDeserializer in = new DataInputDeserializer(out.getCopyOfBuffer());
    return serializer.deserialize(in);
}