product request: dedicated toolhead head board

With the ability for klipper to support multiple MCUs, I'd like to see a product which was a small form factor mcu which just provided the connectivity to drive a single extruder. Perhaps a second product driving 2 extruders.

The single extruder board would provide its own ARM controller plus all of the connectivity needed for a single extruder, 1 stepper driver, hot end power, hot end thermistor, filament sensor, probe, bltouch, and 2 fans

it would not need any connectors for expansion modules, beds, sd cards, rgb, or displays.
Depending on how the tool head is connected to the printer, this could allow for easy removal of the tools with electronics attached as a single package

The issue names no repository files, tests, or implementation entry points. Start by determining whether this repository covers hardware design and how its products relate to Klipper's multi-MCU support; done would require an agreed specification for a single- or dual-extruder toolhead board.

Written by the indexing model from the issue text.