backend selection in o1js

[Trivo25]

we should support both the new native backend as well as provide a fallback to the old wasm backend for the nodejs envrionment - tbd on how to do this

a potential solution would be to provide a new o1js package for this purpose (if we package both wasm and the native artefacts we almost double our package size - not good) - something like import { ... } from '@o1js/node-native' and import { ... } from '@o1js/node-wasm'

[mitschabaude]

it might be nicer to create an API where not all of o1js has to be split in two packages, but most of the current TS is still just o1js and the bindings are injected later:

import { setBindings } from 'o1js'
import nativeBindings from '@o1js/native-bindings'
setBindings(nativeBindings);

// normal code uses 'o1js' imports

[mitschabaude]

^ should work because AFAIK there's no state kept on the Rust side initially, at least in beginning

[dfstio]

There are many cases when proving is not needed, for example, signature verifications, Poseidon hash calculations, tx building (NOT proving). It would make sense to keep the o1js library small to handle such cases and load big proving backend only if needed.