Improve serialization performance of value classes that require only unboxing.

The name of the annotation to be introduced are currently under discussion.
`JsonKUnbox` is the current first choice.

Please refer to the exchange in the comments for restrictions on naming.
If you have a better name, please suggest it.

---

### Use case

In `jackson-module-kotlin`, when serializing a `value class`, even if it is unboxed, the procedure is to box it once and unbox it again if necessary.
This is necessary to enable features such as `JsonValue` and custom serializers.

Since this is done at each serialization call, the performance is greatly reduced compared to using a normal class (`data class` + `JsonValue`).
[Verification with `kogera`](https://github.com/ProjectMapK/kogera-benchmark#normal) confirms this(Although `kogera` is strictly a different project, there are no major differences in processing).

On the other hand, the main use case for the `value class` would be to simply output the `unboxed` value.
In that case, these overheads are completely useless.

### Describe the solution you'd like

I am thinking of providing some way to skip those processes if only unboxing is required.

In my personal experimental project `jackson-module-kogera`, I implemented a way to specify it by means of an annotation named `JsonUnbox`.
https://github.com/ProjectMapK/jackson-module-kogera/blob/develop/src/main/kotlin/io/github/projectmapk/jackson/module/kogera/annotation/JsonUnbox.kt

This annotation is used by attaching it to a `value class` or a `property getter` that returns a `value class`.
https://github.com/ProjectMapK/jackson-module-kogera/blob/e9111c22124f789b66ac0201ce8d8a1156b24110/src/test/kotlin/io/github/projectmapk/jackson/module/kogera/_integration/ser/value_class/json_unbox/ForClass.kt#L9-L11
https://github.com/ProjectMapK/jackson-module-kogera/blob/e9111c22124f789b66ac0201ce8d8a1156b24110/src/test/kotlin/io/github/projectmapk/jackson/module/kogera/_integration/ser/value_class/json_unbox/ForProperty.kt#L18-L39

This is included in [2.15.2-beta5](https://github.com/ProjectMapK/jackson-module-kogera/releases/tag/2.15.2-beta5).

[Benchmarking](https://github.com/ProjectMapK/kogera-benchmark#with-jsonunbox) confirms that it can provide better performance than `data class` + `JsonValue`.

I also considered adding an option to limit the basic behavior regarding `value class` to unboxing, but have not worked on it yet as it would be more difficult to implement.

### Additional context

I am considering implementing the `JsonUnbox` annotation on the `jackson 2.17` target.

Please post any other requests for the name or behavior of this annotation, or for `value class` serialization performance improvements, to this issue.