feat(core): support kotlin.time.Instant

[kangwooc]

Summary

• Add native serializer support for kotlin.time.Instant without adding a kotlinx-datetime dependency.
• Encode as timestamp-millis by default, with writer-schema support for timestamp-micros, timestamp-nanos, and ISO-8601 strings.
• Update the public API dump and reject out-of-range Avro timestamp conversions instead of overflowing or clamping.

Testing

• ./gradlew :core:test --tests '*KotlinInstantEncodingTest' --tests '*KotlinInstantDecodingTest' :core:apiCheck
• ./gradlew check

Closes #417

[Chuckame]

I've been near to merge your PR, however I would have expect the std kotlin.time.Instant to be used, instead of the "additional" other Instant from the kotlinx datetime library, to not depend on another library (not all kotlin projects needs the kotlinX datetime library).

Please adapt it to this kotlin.time.Instant.

If we really want to add support for kotlinx datetime, let's try to propose a modular approach of serializing a timestamp millis/micros/nanos, which would be used by jvm's Instant/Date, the kotlin's Instant, or any other non-kotlin standard time modules. It could be then used on the user-application's side (preferred solution for uncommon time libraries), another avro4k module (preferred for common/official kotlin's libraries, like ktor does), or included in the core lib but optionally (less preferred). Let's put this modularity into another PR 🙏

Thanks again for your work!

[kangwooc]

@Chuckame then do i create another pr and closed this?
if you are okay, i could keep working on this pr.

[Chuckame]

As you prefer, you can reuse this PR also, as mostly only the package name will change in the changes.

[kangwooc]

@Chuckame just for reminder, would you review this?

[Chuckame]

Near to final code, sorry for the delay again