tests: add tests and GHA workflow

[shepherdjerred]

Overview

• Add tests for parser
• Setup GHA for linting + building + testing
• Setup dependabot
• Resolve some linter errors
• Move most of the code into internal

Related to https://github.com/rstudio/package-manager/issues/11950

[shepherdjerred]

@jmwoliver I believe this is all ready!

[jmwoliver]

This looks great! I'd be nice to also test the GPG signing as well if we could. Having a signed .asc file would be in the gpg_signature field from the parser and you'd have to parse the file from the multipart request to make sure it is the same. Here's some rough code on how to do that:

// We may also have 1 and only 1 GPG signature file header
var hasGPG bool
if _, ok := mf.File["gpg_signature"]; ok {
	if len(mf.File["gpg_signature"]) > 1 {
		return errors.New("only one gpg_signature allowed")
	}
	hasGPG = len(mf.File["gpg_signature"]) == 1
}
// Get the file name and size for the GPG data
var fileGPG multipart.File
if hasGPG {
	fileHeaderGPG := mf.File["gpg_signature"][0]
	if fileHeaderGPG == nil || fileHeaderGPG.Filename == "" || fileHeaderGPG.Size == 0 {
		err = errors.New("error retrieving the file name and size from the upload")
		return err
	}
	fileGPG, err = fileHeaderGPG.Open()
	if err != nil {
		return err
	}
	defer fileGPG.Close()
}

You'll also need to cut a new release so that we can pull in these changes to use. That looks like:

git tag v0.3.0
git push origin v0.3.0

[shepherdjerred]

I'll add gpg in another PR since this one is so big!