test: minor improvements to test

[TAG-Epic]

• Lint tests (this will cause a few typing issues which will need to be fixed)
• Improve coverage

Not sure if trying to get a high coverage is worth it, especially with some pretty bad tests.

TODOS:

• [x] Decompressor tests
• [ ] Fix pyright not detecting unused parameters
• [ ] shard tests
• [ ] shard manager tests
• [ ] make tests more reliable (might fail during higher CPU usage)
• [ ] Fix #163 (currently breaking a test)
• [ ] Split decompressor tests
• [x] Testing directly against discord
• [ ] Use a version of pytest-harmony from pypi
• [ ] Redo pytest-harmony to be dependency based