"/sim/signals/fdm-initialized" triggers _every_ time the FDM is reset,
so for every sim reset/relocate.
We need to uninstall the listeners after its first execution, or guard
certain parts of the initialization, to avoid starting multiple
"timer/update loops", or installing multiple property listeners.
Repeating "sim reset" often enough would eventually completely block/
overload the system.
- Update redout level every frame
- Replace reading of properties every iteration with listeners
- move -onset and -complete properties into a parameters subtree
