Draft: Introduce hybrid thinker for conditional nothink + revenge of spike optimisation

This introduces MF_HYBRID: delayed netsafe MF_NOTHINK which shuts it thinker off after a few tics if the object is not in motion. This gets around nothink's various issues by allowing the object to run a scenery thinker for at least a few tics.

Currently only used for floor spikes and cacti.

Before:

After: