Add tests for iOS loop push notifications and websockets

[je-l]

Adds high-level integration tests related to iOS loop push notifications and websocket API. This should help with e.g. dependency updates and to avoid introducing regression bugs when making changes.

Statement coverage increased from 63.8% to 65.4%.
Branch coverage from 51.0% to 53.0%.

[AndyLow91]

Thanks for the PR. The additional coverage looks useful, but I think this needs revision before merge.

A few issues should be addressed first:

• loopnotifications.test.js appears order-dependent around API_SECRET. The suite creates the app using process.env.API_SECRET, but authenticates using a hard-coded hash for a different secret. That makes the test fragile depending on prior test state.
• Both new suites start real Nightscout server instances but do not fully clean them up. Please add proper teardown for the server/bus and any other test resources.
• The fake APNs server uses a fixed port, which makes the test more brittle and can cause avoidable conflicts.

If you can make the new tests fully self-contained and deterministic, I’d be happy to take another look.

[je-l]

Pushed fixes to all three comments, the teardown looks like this now:

after(function(done) {
  inst.server.close();
  inst.ctx.bus.teardown();

  delete process.env.LOOP_APNS_KEY;
  delete process.env.LOOP_APNS_KEY_ID;
  delete process.env.LOOP_DEVELOPER_TEAM_ID;
  delete process.env.ENABLE;

  apn.Provider = OriginalApnProviderClass;

  guardedDrop(inst.ctx.profile(), err => {
    if (err) return done(err)

    fakeAPNServer.close(done);
  });
});

I removed websocket.test.js, the overlap is high with websocket.shape-handling.test.js.
Interestingly, the old websocket tests didn't pass. I think it shouldn't be a regression bug, but I will look a bit more later and create a new issue if needed. For me this PR is ready to merge.