Support for mixing extruders

[JulianStremel]

Is your feature request related to a problem? Please describe

I am currently working on getting mixing extruder support stable in klipper and Kalico(formerly danger klipper).

Describe the solution you'd like

Because fluid already supports multi extruder setups in its toolhead widget i wanted to ask if there would be interest in enabling a more in depth mixing extruder support from the fluid community :)
Mainly i would like to be able to set and see mixing ratios of my extruders as well as track the individual spool usage using spoolman.

Describe alternatives you've considered

Currently i am not using any visualization and i do not have a good way to implement the spoolman feedback but one could consider building macros to set spool usage from within klipper.

Additional information

The original PR on the klipper repo ist stale but i am working on it over at Kalico as i said and i would hope there is interest in the klipper community to push mixing extruders as a viable alternative to ams style systems.

I made a short Video on my custom mixing printer for everybody interested