fix(test): fix ban unit tests to be dependent upon each other

[braindigitalis]

Fixes the ban set/unset/get unit tests to be properly dependent upon each other's callbacks (callback hell, yay) and also to use the IDs of valid users which should never be on a unit test server:

• MEE6
• Dyno
• MidJourney Bot

These 3 will remain valid for the forseeable future. using deleted user ids for bans is not a good idea, they eventually get purged and the side effects of adding bans for them is not doucmented behaviour.

Code change checklist

• [x] I have ensured that all methods and functions are fully documented using doxygen style comments.
• [x] My code follows the coding style guide.
• [x] I tested that my change works before raising the PR.
• [x] I have ensured that I did not break any existing API calls.
• [x] I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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