feat: Resolve oracle calls via JSON-RPC

[sirasistant]

Description

This adds a JSON-RPC client to the DefaultForeignCallExecutor. This allows it to solve unknown oracle calls. The URL to the foreign call executor is an optional argument to nargo execute, nargo test and nargo prove.

Problem*

Resolves #1052

Summary*

Additional Context

An example echo server in typescript

import {
  JSONRPCServer,
  TypedJSONRPCServer,
} from "json-rpc-2.0";
import express from "express";
import bodyParser from "body-parser";

type Methods = {
  echo(params: ForeignCallParam[]): ForeignCallResult;
};

const server: TypedJSONRPCServer<Methods> = new JSONRPCServer(/* ... */);

interface Value {
  inner: string,
}

interface SingleForeignCallParam {
  Single: Value,
}

interface ArrayForeignCallParam {
  Array: Value[],
}

type ForeignCallParam = SingleForeignCallParam | ArrayForeignCallParam;

interface ForeignCallResult {
  values: ForeignCallParam[],
}

server.addMethod("echo", (params) => {
  return {values: params};
});


const app = express();
app.use(bodyParser.json());

app.post("/", (req, res) => {
  const jsonRPCRequest = req.body;
  console.log(jsonRPCRequest);
  // server.receive takes a JSON-RPC request and returns a promise of a JSON-RPC response.
  // It can also receive an array of requests, in which case it may return an array of responses.
  // Alternatively, you can use server.receiveJSON, which takes JSON string as is (in this case req.body).
  server.receive(jsonRPCRequest).then((jsonRPCResponse) => {
    if (jsonRPCResponse) {
      res.json(jsonRPCResponse);
    } else {
      // If response is absent, it was a JSON-RPC notification method.
      // Respond with no content status (204).
      res.sendStatus(204);
    }
  });
});

app.listen(5555);

And the corresponding main.nr

#[oracle(echo)]
fn echo_oracle(_x: Field) -> Field {}

unconstrained fn echo(x: Field) -> Field {
    echo_oracle(x)
}

fn main(x: Field, y: pub Field) {
    assert(echo(x) == y);
}

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [Exceptional Case] Documentation to be submitted in a separate PR.

(We can document this when we evaluate if this solution is enough)

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[kevaundray]

deny.toml is failing because of CC0 license -- we already rely on a CC0 license, so I don't think this is a blocker -- see note in deny.toml as to why we conservatively deny CC0

[kevaundray]

LGTM - was cargo update ran on this branch? most changes are coming from the cargo.lock

[sirasistant]

LGTM - was cargo update ran on this branch? most changes are coming from the cargo.lock

Nope, but i'll reset cargo lock to master and run cargo build again just to make sure