[ENHANCEMENT] Python packaging

[o-murphy]

Hi there! I propose to setup project to be packaged as python module, make it to be installable via pip and runnable via uv and pipx. I can make it and contribute soon.

I would like to participate in the project at least by what I understand

[o-murphy]

Done in #7

• sources refactored to src-based layout
• commented except usage errors
• updated README.md
• build system configured
• added app entry-point
• added dev deps
• added CI workflows for mypy and ruff check
• sources formatted with ruff format