ct-engine: entry point with web bindings

[jsantell]

ct-engine is an entry point consisting of sandboxing, and eventual(?) query planning and scheduling. Initial focus is on web bindings. Some notes:

• Simple case takes ~1ms for execution
• This should be wrapped in a worker. We can expose an interface here that just postMessage's methods to the worker containing CTEngine. Doubly so after removing async handling!

Internals:

• Handful of future cleanups like normalizing the marshaling of types from wasm-bindgen and providing different module/instance lifetimes (TBD on what we'll want)
• Host callback now implemented via closures, with generics removed from Runtime.

  import init, { CTEngine } from './ct_engine.js';

  // Only needed once, call the default export function
  // to fetch and setup the web assembly artifact. 
  await init();

  // Host callback invoked by the VM via `globalThis.hostCallback()`
  const hostCallback = (input) => {
    switch (input.command) {
      case "sum":
        return Array.prototype.reduce.call(input.value, (acc, v) => {
          acc += v;
          return acc;
        }, 0);
    }
    return {};
  };

  // Instantiate an engine
  const engine = new CTEngine(hostCallback);

  // Define a module definition
  const definition = `
export const run = (input) => {
  input.foo = input.foo + 1;
  input.bar = globalThis.hostCallback({
    command: "sum",
    value: [1, 2, 3],
  });
  return input;
};
`;

  // Instantiate the module.
  let id = engine.define(definition);
  // Call the module function.
  var output = engine.run(id, { foo: 9 });

  console.log("Output:", output);
  console.assert(output.foo === 10);
  console.assert(output.bar === 6);