Fallback Id handler to handle migration from 8-byte ids to 4-byte schema ids

[ozangunalp]

During the testing of quarkusio/quarkus#51401, we realised that the migration to v3 involves handling the change of schema ids from using 8-bytes to 4-bytes.

While there are distinct IdHandler implementations available to the client application to use, there isn't any easy migration path to use with message processing applications producing/consuming on topics (eg. Kafka).

The problem of an active topic is explained here : quarkusio/quarkus#51401 (comment)

This change proposes an OptimisticFallbackIdHandler to write 4-byte ids and read both 4 and 8 byte ids to be used in a migration scenario.

Because the payload format doesn't include any format versionning, this IdHandler makes the following assumption to distinguish between 4-bytes 8-bytes ids: The schema ids are greater than 0 and smaller than integer max value.

The change requires some non-breaking modifications to AbstractDeserializer, and maybe to the IdHandler interface that can be discussed.

Additionally, I couldn't figure out what to do for the Go SDK.

[ozangunalp]

@carlesarnal fyi

[carlesarnal]

Thanks for the PR, as we've discussed, this addresses a real migration pain point for v2 → v3 upgrades. I think the approach makes sense, but it's probably worth documenting the assumptions as javadoc in the OptimisticFallbackIdHandler class.

[ozangunalp]

@carlesarnal I've added some docs for the Id handler class