Consider applying armor to all damage

Right now armor is not applied to collision damage. This leads to surprising behaviour where units can still get damaged despite setting the multiplier to 0. I don't expect any game would mind since collision damage is very rare (ZK involves lots but we override it in a gadget anyway) but it would be good to ask beforehand.
https://github.com/beyond-all-reason/RecoilEngine/blob/7363dbc54b55d309539b92c60245f88afd1f4e4a/rts/Sim/Units/Unit.cpp#L1298-L1306

Start in rts/Sim/Units/Unit.cpp at lines 1298-1306 and trace how collision damage is handled compared with other damage types. Check the relevant damage behavior and confirm that collision damage respects the configured armor multiplier, including a multiplier of 0.

Written by the indexing model from the issue text.