feat: Added !hidemode command

[AcaroMan]

Adds !hidemode command to allow players to hide item holders and even leaders.
Players can cycle or directly set the mode.
Using the command doesnt directly toggle hide state.
Functionality will help for lazer sections and maps with lots of items.

Issue: Just like when a player is glowed and it enters hide range and the glow stays on the last spot, the same happens with items as they seem to get stuck in the place until the hidden item holder is not within hiding distance anymore.

[Vauff]

Not allowing leaders/item holders to be hidden is intentional, because those additional entities parented to a hidden player will become permanently desynced for the rest of the round. This can introduce gameplay issues for example with items that are supposed to toggle effects on use etc.

Theoretically this could be overcome by implementing more in-depth hierarchy tracking, but this would also somewhat increase hide crash rates again, as more entities would be getting hidden. It'd probably also only make sense to do this with a larger overhaul moving more hidden player calculation out of the CheckTransmit callback for optimization purposes (like CheckHideDistances is).