VR/Hall mixing test board

Problem statement: do do not have x8 or x10 position sensor inputs on stm32, in order to handle any combination of x5 hall and x3/x5 VRs we would need to mix each VR with Hall

We are looking to confirm that VR signal (in this case from MAX9924) could be mixed with Hall signal into same/shared digital signal

![image](https://github.com/rusefi/rusefi-hardware/assets/48498823/58c52c42-db98-45c9-baec-19b8690e5c79)