Really modular backends

[one-some]

• [ ] Adding backends should be super dead simple for sharability of backends that aren't upstreamed
• [ ] User should be able to choose what backend to use, different models will appear based on which one was selected

[one-some]

let's try to make model selection ux not so weird since we'll have to have multiple backends and stuff

1. Pick model
2. Ask all backends if they support it
3. if so add them to the list
4. if user accepts the backend load