ci: Set up CodeQL analysis w/ fixes

[erisu]

Motivation and Context

CodeQL scanning in CI can help identify bugs and security issues with the library.

Description

• Added CodeQL scanning with default options as part of CI.
• Include fixes

Testing

• Ran this in my fork, confirmed that CodeQL results showed up under security scanning
• Applied some small fixes

Checklist

• I've run the tests to see all new and existing tests pass

[github-advanced-security]

This pull request sets up GitHub code scanning for this repository. Once the scans have completed and the checks have passed, the analysis results for this pull request branch will appear on this overview. Once you merge this pull request, the 'Security' tab will show more code scanning analysis results (for example, for the default branch). Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results. For more information about GitHub code scanning, check out the documentation.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.15%. Comparing base (b773ae4) to head (ebab8ae).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1711      +/-   ##
==========================================
- Coverage   72.35%   72.15%   -0.20%     
==========================================
  Files          23       23              
  Lines        1834     1839       +5     
==========================================
  Hits         1327     1327              
- Misses        507      512       +5     

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