Fix KafkaSource generic type and improve SunsetAirFlightData deserialization test

[DavidGonzalezPineiro]

Description:

The KafkaSource for sunsetSource uses an incorrect generic type. The SunsetAirFlightData does not perform full equality checks after JSON deserialization.

Expected:

• Correct generic type in KafkaSource (SunsetAirFlightData).
• Tests that fully verify deserialization, including correct handling of time zones and unknown fields.
• Update the reference in https://developer.confluent.io/courses/flink-java/merging-flink-data-streams-exercise/ page