`gadget:AllowUnitTransport` can technically desync

`AllowUnitTransport` is synced but can be called from unsynced, here's a "trace":

https://github.com/beyond-all-reason/RecoilEngine/blob/604f00d290a2e3ddbc2fae9f27f10b9c8efedc0a/rts/Lua/LuaHandleSynced.cpp#L818
https://github.com/beyond-all-reason/RecoilEngine/blob/604f00d290a2e3ddbc2fae9f27f10b9c8efedc0a/rts/Sim/Units/Unit.cpp#L2549-L2558
https://github.com/beyond-all-reason/RecoilEngine/blob/604f00d290a2e3ddbc2fae9f27f10b9c8efedc0a/rts/Sim/Units/CommandAI/MobileCAI.cpp#L937-L946
https://github.com/beyond-all-reason/RecoilEngine/blob/604f00d290a2e3ddbc2fae9f27f10b9c8efedc0a/rts/Game/SelectedUnitsHandler.cpp#L868-L900
https://github.com/beyond-all-reason/RecoilEngine/blob/604f00d290a2e3ddbc2fae9f27f10b9c8efedc0a/rts/Game/UI/GuiHandler.cpp#L1679-L1708

Reproduction:

* take https://github.com/ZeroK-RTS/Zero-K/tree/artificial-allowunittransport-desync (makes `AllowUnitTransport` reduce health)
* build a transport (e.g. `gunshiptrans`), select it (so that the load command is checked), hover over some units. Whatever you hover over something, it loses health
* watch the replay and keep your cursor away. Units don't lose health

This has been the case perhaps forever, so it most likely not related to the recent desyncs. ZK's real `gadget:AllowUnitTransport` adds units to a cache like this:
```lua
if allowTransportCache[transporterUnitDefID][transporteeUnitDefID] then
return (allowTransportCache[transporterUnitDefID][transporteeUnitDefID] == 1)
end
local allowed = not UnitDefs[transporteeUnitDefID].customParams.requireheavytrans
allowTransportCache[transporterUnitDefID][transporteeUnitDefID] = ((allowed and 1) or 0)
return allowed
```
This does not affect unit positions etc., only the contents of that `allowTransportCache` table which affects nothing downstream (since on a "real" call later it would get filled with the same value anyway), so I somewhat doubt that this can actually trigger the desync warning either. But the capability is there and IDK about other games.