make this compatible with the new external raster mask

[urbach]

With the new external raster mask module in darktable 5.2 it would be interesting to add a feature to save the mask generated by SAM2 as a PFM file.

It should not be too difficult to adjust, however, currently I'm failing at the 'poetry install' step with

  RuntimeError

  The Poetry configuration is invalid:
    - Additional properties are not allowed ('group', 'package-mode' were unexpected)


  at /usr/lib/python3/dist-packages/poetry/core/factory.py:43 in create_poetry
       39│             message = ""
       40│             for error in check_result["errors"]:
       41│                 message += "  - {}\n".format(error)
       42│ 
    →  43│             raise RuntimeError("The Poetry configuration is invalid:\n" + message)
       44│ 
       45│         # Load package
       46│         name = local_config["name"]
       47│         version = local_config["version"]