Provide the VegaFusionRunTime from the vegafusion package

[MarcSkovMadsen]

The only dependency the panel-vegafusion python package has to vegafusion python packages is the import of the vegafusion_jupyter.runtime.

The runtime is an instance of the VegaFusionRunTime defined in vegafusion_jupyter.

I believe its more natural that the VegaFusionRunTime is defined in the vegafusion package. In that way integration libraries have a more simple and natural dependency.

If not it would make sense for me to copy the VegaFusionRunTime implementation to panel-vegafusion package and drop the dependency on vegafusion_jupyter.

Please let me know what you would prefer @jonmmease ? Thanks.

[jonmmease]

Yeah, there are a couple of things that should be moved out of vegafusion-jupyter. In addition to the runtime, the data transformer that writes DataFrames as feather files will apply across extension types.

Right now vegafusion-python is a pure Rust package and I haven't yet worked through how to combine pure Python modules in the same package. I doubt it's that difficult, but I haven't tried. In any case, I'd say go ahead and copy over what you need right now, and that will help inform the refactoring later.