add completions to cli

[drmorr0]

• [x] I certify that this PR does not contain any code that has been generated with GitHub Copilot or any other AI-based code generation tool, in accordance with this project's policies.

Description

Adds a new subcommand to generate shell completion files

Testing done

• manual testing
• new tests

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 38.57143% with 43 lines in your changes missing coverage. Please review.

Project coverage is 72.28%. Comparing base (42f146c) to head (92d6495).

Files	Patch %	Lines
cli/completions.rs	42.85%	36 Missing :warning:
cli/main.rs	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #121 +/- ## ========================================== - Coverage 73.14% 72.28% -0.86% ========================================== Files 39 40 +1 Lines 2245 2309 +64 ========================================== + Hits 1642 1669 +27 - Misses 603 640 +37 ```

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