Extract Mineflayer test API into standalone module #1422

Is your feature request related to a problem? Please describe.

Unit testing plugins can be messy and creates lots of redundancy and boilerplate code. Most external plugins rely on the exact same testing strategy as internal plugins. It would make sense to extract test API into a standalone Prismarine module that can be used by Mineflayer and external plugins to improve long-term stability.

Describe the solution you'd like

The module should include node-minecraft-wrap as well as some helper APIs for removing boilerplate test code that specifically involves high-level testing within Minecraft servers. This should be something easy to add as a dev-dependency for running tests locally and within the CI.

All tests usually involve the same pattern of downloading and running a vanilla Minecraft server, then loading a bot into that server and having it perform some quick actions, validating those actions, then disconnecting. This kind of process can be greatly simplified to the end-user.

Describe alternatives you've considered

Testing manually on each repo. However, this creates too much redundancy.

Additional context

This feature was discussed in the Discord server and was overall well received.

In addition, this might improve long-term stability across many PrismarineJS repos and plugins. There are several long-lived issues that might be able to be crossed off as well. Lastly, using an external module would make debugging easy if the module was configurable, as more intense local tests can be performed using commands without clogging up the CI. Some examples of this could be optionally downloading with Spigot or Paper instead of vanilla in order to test against certain plugins. All of this could be configured from the command line.