facebook/rocksdb ? reverse-engineered prompt

Build me a C++ library for a fast embedded key value store that keeps data on disk and can be used inside another app. It should handle large amounts of data well, work smoothly with flash and RAM storage, and be designed for fast writes and reads with good reliability. I want a clean public API that other programs can use without needing to know the internal details, plus a few simple example programs that show how to open a database, write values, read them back, and close it safely.

Please include solid tests, clear build instructions, and enough documentation so someone can get started quickly. If you need to check current best practices or API details online, do that. Make sure it feels like a real production library, not just a demo, and organize it so the main user facing pieces are easy to find.