Feature/just - Add just command runner

[use-the-fork]

This pull request introduces the Just command runner and integrates it directly into devenv.

Key Additions:

• Implements the Just command runner directly into devenv script. (can be turned on by adding just.enable = true; to a script)
• Integrates with devenv up, and version.
• Includes sample Just scripts for initial use and further development.
• Adds the default justfile, which imports just.flake into REQUIRED_FILES for proper setup.
• Updates documentation to include new options and settings for the Just command runner.

The final result looks like this:

Issues Addressed:

• Closes #739
• Closes #117