Draft: Resolve "Vet testing in `completion`"
General MR
Summary
- Refactored all tests into one test func "TestAllCompletions", left "TestFooCompletion" for future reference
- Added powershell into the list of valid shells, added corresponding comments to load powershell completions for the session, and added corresponding test
- Removed all other unnecessary tests that were refactored into "TestAllCompletions"
- Updated Bash completion to V2, as the previous version was legacy
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Linked Issue
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Closes #68 (closed)