unified color interface

[tontyoutoure]

1. unified color interface in c++ and python
2. volume color can take color name now, like "red", "blue"

I'm not sure whether this is necessary, since there is only that much visualization in Gate 9. But this surely conforms the DRY principle better.

[dsarrut]

Hi @tontyoutoure,

Thank you for this PR. Having named colors for volumes (vol.color = "red") is indeed a welcome improvement and simplifies user scripts nicely.

There is just one bug to fix in opengate/geometry/volumes.py where self.color[3] is accessed directly:

        self.g4_vis_attributes.SetColor(
            *validate_color(self.color, f"Color error for volume {self.name}: ")
        )
        self.g4_vis_attributes.SetVisibility(bool(self.color[3]))

If a user specifies a short color name like "red", self.color[3] raises an IndexError: string index out of range (it only worked for "magenta" in the test because len("magenta") > 3).

Please store the result of validate_color in a local variable:

        color = validate_color(self.color, f"Color error for volume {self.name}: ")
        self.g4_vis_attributes.SetColor(*color)
        self.g4_vis_attributes.SetVisibility(bool(color[3]))

Also, in GateHelpersDict.cpp, DictGetColourVec appears to be an undeclared alias for DictGetVecColour that can be removed.

Once these points are addressed, this is good to merge.

David (review made with AI)