Optimize flow processing code

[nerdoug]

Our efforts at monitoring CPU usage show that the flow processing takes a significant portion of the CPU. This may become more of an issue as additional functionality is added, especially if there's a need for quick response to events. One way to minimize the impact is to optimize the efficiency of flow processing coding, including steps like:

• moving constant calculations out of loops
• avoiding floating division (multiply by reciprocal instead) because the ESP32 FPU is particularly slow at division
• unrolling loops ( although trading off for memory use isn't ideal when we're using a lot of memory at the moment)
• reducing unproductive generality. For example, looking up the number of legs on the robot in a variable can be replaced by a macro which can be optimized by the compiler
• using inline routines where practical, and not too expensive for memory
• using conditionals to remove debugging and diagnostic code for "production" software
• using integers rather than floating point when practical