🌴 Jumanji compatability

Train rejax agents on Jumanji environments!

• Added rejax.compat.jumanji2gymnax, create Jumanji environments via rejax.compat.create("jumanji/...")
• Dropped support for Python 3.9 (it might still work but we now want flax 0.9, which requires 3.10)
• Updated configs and added tests to make sure they are valid
• Changed build system to use pdm
• Changed package layout to use source layout and renamed test folder to tests

Full Changelog: v0.1.0...v0.1.1