Improve development setup

[dlqqq]

Description

• Fixes hatch environment setup
• Adds playground/ directory
• Corrects and expands on README.md

Testing

• Fetch and checkout this branch locally
• Follow instructions in README.md to verify development setup process

Known issues

• jlpm setup:dev when run as a post install command does not properly link labextensions
  • Partly because setup:dev requires build, which fails because of incompatible @jupyterlab/builder versions, which fails because hatch doesn't seem to respect build dependencies
  • Likely also due to different application directory (jupyter lab path) during installation procedure
• Pressing Ctrl-C to shut down Jupyter Server in hatch shell causes really weird behavior where Jupyter Server continues to run in background and prints output to terminal
  • Requires further investigation
  • Server can be killed manually by finding its PID with ps u and then doing kill <PID>.
  • This seems to fail freeing up the port though; Jupyter Server bug?

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[krassowski]

This seems to fail freeing up the port though; Jupyter Server bug?

I see this often but it did not reproduce reliably for me. I am not sure what is happening but indeed likely not related to work in this repo