Activate custom gates in JS and add rangeCheck64 gadget

[mitschabaude]

closes #1172

bindings: o1-labs/o1js-bindings#179

This PR

• adds logic to the Wasm bindings to infer feature flags from a verifier index
  => makes Kimchi verification work for proofs that use custom gates
• dynamically passes the right feature flags to Pickles.compile based on the gates used in a circuit
  => makes Pickles proofs work with custom gates
• to test that this works, exposes the rangeCheck0 gate to JS, and wraps it in a 64-bit range check gadget
• uses that gadget in UInt64, which is very well covered by existing tests

TODOs:

• understand performance impact on example zkapps and possibly remove custom gate from UInt64 again, or move it behind a customization flag
• changelog and documentation about the new gate

UPDATE
Following internal discussion, I didn't use the rangeCheck64 gate in UInt64 for now. Thus, there is no more test in this PR that everything works (but CI for a previous commit shows it working)
However, there is now a follow-up PR which exposes the new gate directly (for advanced users), and also adds a unit test: #1181

[MartinMinkov]

Looks great to me! 🎉

[MartinMinkov]

nit: This is a superficial suggestion, but you could add some type safety here instead of the switch statement

const gateTypeToFlagKey: Record<GateType, keyof FeatureFlags> = {
  RangeCheck0: 'rangeCheck0',
  RangeCheck1: 'rangeCheck1',
  ForeignFieldAdd: 'foreignFieldAdd',
  ForeignFieldMul: 'foreignFieldMul',
  Xor16: 'xor',
  Rot64: 'rot',
  Lookup: 'lookup',
  ...
};
  
for (let gate of gates) {
  const flagKey = gateTypeToFlagKey[gate.type];
  if (flagKey) {
    flags[flagKey] = true;
  }
};

[mitschabaude]

fwiw I think the switch statement is perfectly type-safe

but your suggestion is definitely less spaghetti-like than the long switch statement

[mitschabaude]

I went with the object approach. This is the type signature you need to encode that some but not all gate types cause a feature flag to be set (same as the switch statement with the default branch):

const gateToFlag: Partial<Record<GateType, keyof FeatureFlags>> = {
  RangeCheck0: 'rangeCheck0',
  RangeCheck1: 'rangeCheck1',
  // ...

[MartinMinkov]

// not using compact mode
why not? 😅

[mitschabaude]

this is just a different "mode" of the gate which is used in specific circumstances (when combining this with other gates to do a 2x88 + 1x88-bit range check where the 2x88-bit value is what is called "compact")