Add devenv

[straight-shoota]

Enables linting for typos (#23) and markdownlint (#22) and others, to ensure continued quality.

The CI workflow automatically checks changes. It's based on the version from the Crystal repo and includes the latest update from crystal-lang/crystal#16682.

[ysbaddaden]

Can't we just add a couple actions? I mean:

jobs:
  lint:
    - name: typos
      uses: crate-ci/typos@v1.44.0

    - name: markdownlint
      uses: DavidAnson/markdownlint-cli2-action@v22

There's no point into installing nix, devenv and all their dependencies just to run a couple executables to check typos in markdown files.

[straight-shoota]

I agree. We could do that as well. 🤷

But I believe there is a benefit in standardizing our infrastructure. If all repos have a lint workflow driven by the devenv configuration, it's easier to maintain and reason about. If we want to add a new linter, it's clear where it should go. And we can easily scale that across all repos.

I also very much like that we can easily run exactly the same linter outside of CI, for example as pre-commit hook. That avoids any annoying disagreement between local pre-commit and CI caused by different versions.

I'm not committed too much to this solution. I just find it's not worth it to do something different here.
The important thing is to setup some automated linking, whatever the means.

[straight-shoota]

Speaking about standardization, this repo used main as default branch, whereas it's master in all other repos. That's just confusing, so I changed it to the standard.