MagicStack: use Multimap for Spells Cast

[Hanmac]

Still WIP

I'm refactoring how "ThisTurnCast" stuff is stored.
If it is done as ListMultimap, using Player as Map-Key, then we don't need extra counting.

and if we store ThisGameCast too, then we can clean up some other stuff.

[Hanmac]

@tool4ever @MostCromulent
I want to find a way to copy the castThisTurn/LastTurn/ThisGame in GameCopier and GameSnapshot

for this i probably need to copy the LKI again to replace the oldPlayer with newPlayer (and maybe the host cards too?)