ByteEntropyDotCom/iso8583-iso20022-mapper-core ? reverse-engineered prompt

Build me a Java 21 Spring Boot service that acts as a bridge from ISO 8583 payment messages to ISO 20022 XML.

I want one endpoint that takes a JSON request with a transaction id, a source region, the raw ISO 8583 payload, and some metadata, then returns a clean XML document in the ISO 20022 style. It should handle different regional payment formats, like UK FPS, Singapore FAST, and US FedNow, in a way that makes it easy to add more later without rewriting everything.

Make it fast and ready for high traffic, using virtual threads if that fits, and keep the models simple and immutable where possible. Include basic validation, clear content handling for JSON in and XML out, plus tests so the mapping logic is reliable. If needed, look up current docs online and set it up so it can run locally and in Docker.