build(requirements.txt): separate development dependencies

[mion00]

Description

Development dependencies are specified in their ad-hoc file

Motivation and Context

• fixes: #172

How has this been tested?

By running locally in a VSCode dev container

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Enhancement (non-breaking which updates existing code)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Other

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.