build(workflow) to check code format adheres to air.toml specs

[andybeet]

Your commits explain the what and where you made changes in the code. Your commit messages explain why you made the commits. You do not need to reiterate this. This PR is meant to address the big picture, Why

Justification 🐟

Need a workflow to run atomated checks on code formatting. This PR uses a GitHub action from the posit folks to do this
fixes #53

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

Checklist/Reminders

Put an x in the boxes that apply

• I have updated relevant documentation?
• I have tested my changes?
• I have created unit tests and run devtools::test() to ensure all unit tests pass locally?
• I have run devtools::check() to ensure package builds locally?
• I have followed the proposed CONTRIBUTING guideline?

Further comments

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Reviewer instructions:

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