Initial migration away from JAXB annotations

[jeandersonbc]

Description
Since the underlying serializer relies on Gson lib, we are unable to use directly Jackson annotations since they don't work as expected. This was verified via test coverage. Furthermore, the required=true validation was never enforced (see AbortRequestTest tests).

Tested scenarios

• Serialization/Deserialization from external file
• Missing required fields (that are not enforced in practice)

[gemini-code-assist]

Code Review

This pull request migrates several Nexo model classes, including AbortRequest, DisplayRequest, LoginRequest, and MessageHeader, from JAXB XML annotations to GSON @SerializedName annotations. The changes also involve removing JAXB-specific metadata and adding unit tests to verify that serialization and deserialization remain functional even when fields previously marked as required are missing from the JSON payload. I have no feedback to provide.

[thomas-cools]

@jeandersonbc is my understanding correct that we were using the jaxb annotation with GSON as the serializer / deserializer, so there is no actual change in behavior other than using GSON annotations?

[jeandersonbc]

@jeandersonbc is my understanding correct that we were using the jaxb annotation with GSON as the serializer / deserializer, so there is no actual change in behavior other than using GSON annotations?

Correct @thomas-cools (cc @gcatanese)! I also pushed this test that verifies how GSON handles the JAXB annotations. The target class (EventNotification) has not been migrated and has some required=true fields. If those checks were really enforced, EventNotificationTest would have failed.

I'm going to proceed to JAXB -> Gson annontations as part of the original task.