Register classes based on ctor

[tswast]

When I get a node from a graph, the graph should return a nice object (custom class) when one exists for it.

I think a class decorator could be used to register classes globally and associate them with a specific value for ctor.

@pikov.register_class(ctor=bytes.fromhex("8b057dd7a9c84b7180cb2d8d6015b833"))
class Frame(SemanticGraphNode):
    def __init__(self, guid_map, guid=None):
        super().__init__(names["frame"], guid_map, guid=guid)

    duration_microseconds = Int64Property(names["frame.duration_microseconds"])
    bitmap = BitmapProperty(names["frame.bitmap"])

    def _to_img(self):
        image_url = self.bitmap._to_data_url()
        if not image_url:
            return None

        return (
            f'<img alt="clip preview" '
            f'src="{image_url}" '
            f'style="width: 5em; {PIXEL_ART_CSS}">'
        )