Small package updates

[almathew]

As per the discussion I started in Slack, this doesn't go quite as far as I would've hoped in updating things given that there's a few open questions about how to move forward.

This instead only -

• Drops aptible-tasks which gets us one step closer to fully deprecating that
• Switches linting to the "new" approach (that's been around for a few years at this point)
• Updates to just testing Ruby 3, since we've been on just 3 for a while now
• Adds docker-compose / just based testing for local development

Overall, most of the changes are from rubocop -a.
There's one weirdo bit with spec/fixtures/app.rb where the correct thing to do is use Auth stubs correctly, but since it's a pretty minimal use case, I did the bare minimum instead.

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[UserNotFound]

Looks good, but we should bump the version to 1.0.2 so we can also release it.

[almathew]

Looks good, but we should bump the version to 1.0.2 so we can also release it.

See this 😉

As per the discussion I started in Slack