Improve requirements

[AlexAndorra]

• Added main requirements explicitly to requirements_dev.txt
• Created a mirror env_dev.yml, to enable mamba installation for developers
• Added jupytext for easier review and conflict resolution of Jupyter NBs
• Fixed typo in requirements-dev.txt: myp --> mypy

Concretely, that means developers can install BayesFlow in at least 2 ways:

• pip:

  mamba create --name bf-dev python=3.11
  mamba activate bf-dev
  pip install -e .
  pip install -r requirements_dev.txt

• Full mamba (which I usually prefer if any compilers are needed):

  mamba env create -f env_dev.yml
  mamba activate bf-dev
  python setup.py develop

Ready for review 🍾

[LarsKue]

Thank you for the PR. One minor comment: Ideally, I think we should have version specifiers ~= on all dependencies that allow it (i.e., not on tensorflow at the moment, since we require <2.16). I'm happy to merge as-is as well, though.

[AlexAndorra]

Up to you @LarsKue -- I'll follow your experience