Remove uses of JS classes in OCaml, Part 1

[mitschabaude]

bindings: o1-labs/o1js-bindings#34

follow up PR to #902, #932, #935

this works towards removing the ocaml Field and Bool classes, by moving to lower level field representations in ALL APIs exposed from ocaml, except Field and Bool themselves. For example, this changes the Poseidon and Pickles APIs, and various helpers. TS to ml conversion logic is moved to TS, to keep the ml side as light as possible.

We also continue the work of #935 of moving helper functions on Ledger to a Test module and relegating them to consistency tests (while using TS impls in snarkyjs)

Note: this PR doesn't yet remove old Field and Bool to keep it independent from the Bool refactor #936