Provide exactly one handler for events and another for fatal errors

[ptpaterson]

Ticket(s): FE-4969

Small breaking change, but looking for feedback first. Compared to the callback example in #232, this would remove the concept of registering one or more callbacks before the start method. There is no adding or removing of callbacks, and no more no ambiguity about how the async interface should work if you have registered callbacks. Here is a modified example:

import { Client, fql } from "fauna"
const client = new Client({ secret: FAUNA_SECRET })

const stream = client.stream(fql`MyCollection.all().toStream()`)

stream.start(
  function onEvent(event) {
    switch (event.type) {
      case "start":
        console.log("Stream start", event);
        // ...
        break;

      case "update":
      case "add":
      case "remove":
        console.log("Stream update:", event);
        // ...
        break;
    }
  },
  function onFatalError(error) {
    // An error will be handled here if Fauna returns a terminal, "error" event, or
    // if Fauna returns a non-200 response when trying to connect, or
    // if the max number of retries on network errors is reached.

    // ... handle fatal error
  }
);

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[ptpaterson]

Personally, I like how this harmonizes the sync and async APIs

async

const stream = client.stream(fql`MyCollection.all().toStream()`)

try {
  for await (const event of stream) {
    handleEvent(event)
  }
} catch (error) {
  handleFatalError(error)
}

sync

const stream = client.stream(fql`MyCollection.all().toStream()`)

stream.start(
  handleEvent(event),
  handleFatalError(error)
)