[CI] add nilaway check

[AshleyDumaine]

This adds nilaway and addresses issues that were caught by it or suppresses irrelevant errors

General:

• Have you removed all sensitive information, including but not limited to access keys and passwords?
• Have you checked to ensure there aren't other open or closed Pull Requests for the same bug/feature/question?

Pull Request Guidelines:

1. Does your submission pass tests?
2. Have you added tests?
3. Are you addressing a single feature in this PR?
4. Are your commits atomic, addressing one change per commit?
5. Are you following the conventions of the language?
6. Have you saved your large formatting changes for a different PR, so we can focus on your work?
7. Have you explained your rationale for why this feature is needed?
8. Have you linked your PR to an open issue

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.03%. Comparing base (52dbb71) to head (fb1f520).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
cloud/linode/services/firewalls.go	0.00%	2 Missing and 1 partial ⚠️
cloud/nodeipam/ipam/cloud_allocator.go	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #486      +/-   ##
==========================================
- Coverage   72.09%   72.03%   -0.06%     
==========================================
  Files          19       19              
  Lines        3652     3655       +3     
==========================================
  Hits         2633     2633              
- Misses        779      781       +2     
- Partials      240      241       +1     

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