A lot of the helpers in `helpers.ts` are heavily bound to NodeJS and at
the moment we're trying to make the `Connection` class be able to run in
multiple environments. Its only remaining Node dependency was its
reliance on `helpers.ts`, which it only needed for `assert`.
This is a useful change also because `helpers.ts` is quite large and
full of functions that do different things; I think we can name them
better and move them into modules with a specific purpose rather than a
generic `"helpers"` dumping ground.
Once this change lands `Connection` should be usable in the browser.
We should import them just like any other module. This commit makes that
change. It does not change any behaviours or the types themselves.
EXPECTED_PROTOCOL_DIFF as we're updating the structure of it.
