This looks like a great idea, and good work in implementing it and developing clear documentation.

There is a huge downside though, this ORM doesn't implement any of the real-time features which makes Firestore so appealing in the first place. Snapshot changes is one of the best things about Firestore, allowing realtime database updates to appear on the client. By not using this feature this becomes indistinguishable from any other database backend...

There's also a major limitation without using Batched transactions. As Firestore limits you to 500 updates per request, which comes up pretty fast in a lot of systems.

Sorry to be so critical, genuinely like the efforts made, just thought I'd mention why those features are important.