Add unit testing for all routes/interactions

[MattIPv4]

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Using https://github.com/dollarshaveclub/cloudworker, unit tests should be implemented for all the HTTP routes in the worker.

For interactions, there should be unit tests to ensure that the verification middleware works as expected, and then unit tests should be provided for each command in the interactions app.

[MattIPv4]

Given that cloudworker is now abandonware, using https://miniflare.dev/recipes/ava.html is likely a better bet here.

[MattIPv4]

Started work on this in https://github.com/MattIPv4/DNS-over-Discord/tree/testing -- will likely implement the patterns needed for testing & add basic tests for http routes, but create a follow-up issue for testing the actual interactions logic.