move ddlpy to pixi

Inspiration:
- https://github.com/Deltares/dfm_tools/issues/981
- https://github.com/Deltares/hydromt_delft3dfm/issues/210, https://github.com/Deltares/hydromt_delft3dfm/issues/261, https://github.com/Deltares/hydromt_delft3dfm/issues/252
- overview: https://github.com/Deltares/hatyan/issues/431