Restructure o1js/src/lib

[mitschabaude]

restructure files in src/lib

close #1329

src/lib/
  mina/ # everything that has to do with mina (=> no dependencies into this folder from others!)
  proof-system/ # zk proving tooling, like Circuit and ZkProgram
  provable/ # everything that has to do with writing provable code (and is not mina-related)
    core/ # low-level, wrappers around snarky-ml
    types/ # provable type intf, methods to create provable types
    gadgets/ # what it used to be
    crypto/ # crypto-related circuits / types like PublicKey and Poseidon
    tests/ # all tests that used to be next to one of the files in /provable
    # other circuits at the top level here
  testing/ # what it used to be
  ml/ # helpers to talk to JSOO
  util/ # everything else

bindings: o1-labs/o1js-bindings#259

[Trivo25]

super clean!