ad-kat/sdk-java ? reverse-engineered prompt

Build me a Java SDK for Temporal so developers can write workflows and activities in plain Java and run them against a Temporal server.

I want the core library to let people create workflow clients, define workflow interfaces, implement activities, and have good test support with a local test server or time skipping test mode. It should also include a simple Spring Boot integration, so apps can wire the SDK in without a lot of setup. If it makes sense, include a small helper module for service client config and a way to work with protobuf based payloads cleanly.

Please make it feel like a real production library, with tests, docs, and a build that works from the command line. Keep it compatible with modern Java, and if you need to check current Temporal docs or examples online, go ahead.