* refactor(REST): remove double classing
BREAKING CHANGE: `REST` and `RequestManager` have been combined, most of the properties, methods, and events from both classes can now be found on `REST`
BREAKING CHANGE: `REST#raw` has been removed in favor of `REST#queueRequest`
BREAKING CHANGE: `REST#getAgent` has been removed in favor of `REST#agent`
* chore: update for /rest changes
BREAKING CHANGE: NodeJS v18+ is required when using node due to the use of global `fetch`
BREAKING CHANGE: The raw method of REST now returns a web compatible `Respone` object.
BREAKING CHANGE: The `parseResponse` utility method has been updated to operate on a web compatible `Response` object.
BREAKING CHANGE: Many underlying internals have changed, some of which were exported.
BREAKING CHANGE: `DefaultRestOptions` used to contain a default `agent`, which is now set to `null` instead.
