fix(model): avoid adding timeout on Model.init() buffering to avoid unintentional dangling open handles

[vkarpov15]

Fix #15241

Summary

Make Model.init() skip buffering timeouts introduced in #15229

Based on discussion from #15241, I think this is a reasonable approach which gives us the benefits of #15229 without the implicit dangling handles. The following Jest test won't complain about open handles:

const mongoose = require('mongoose');

// Define a User schema and model
const userSchema = new mongoose.Schema({
  name: String,
  email: String,
  age: Number
});

const User = mongoose.model('User', userSchema);

describe('Database connection', () => {
  it('test', function () {

  });
});

However, the following script will still error out with buffering timeout, as opposed to silently exiting with no error.

'use strict';

const mongoose = require('mongoose');

(async function() {
  await mongoose.connection.listCollections();
})();

So explicit connection helper calls will be subject to buffer timeouts, but we will ignore buffer timeouts for Model.init() because Model.init() is called implicitly and there are use cases where you may want to create a model without opening the underlying connection, like testing document functionality.

Examples

[hasezoey]

Can confirm this fixes the cases i had for typegoose without needing to set any options or other code changes.

[hasezoey]

I think this could be de-duplicated by storing the promise in a variable before the if, and just directly awaiting it here and in the other branch adding it to the race.