Clean up ros3 VFD stats code

[derobins]

• Removes printf debugging
• Simplifies and centralizes stats code
• Other misc tidying

[derobins]

The actual changes are smaller than appears, due to git being confused. You can look at the individual commits to see what I was doing.

FWIW, the stats code didn't even compile when I started working on it. I'll look into adding it to developer mode and/or CI in a future PR.