Break circular dependency in Context

[jemrobinson]

✅ Checklist

• You have given your pull request a meaningful title (e.g. Enable foobar integration rather than 515 foobar).
• You are targeting the appropriate branch. If you're not certain which one this is, it should be develop.
• Your branch is up-to-date with the target branch (it probably was when you started, but it may have changed since then).
• You have marked this pull request as a draft and added '[WIP]' to the title if needed (if you're not yet ready to merge).

⤴️ Summary

Add ContextBase class to break circular dependency

🌂 Related issues

Closes #1852

🔬 Tests

Tested locally

[JimMadge]

@jemrobinson Sorry, should have asked when reviewing, could you add a test which uses the top level Typer to show that this PR fixes the issue? (Could, for example, just run dsh --help)