feat(battle-engine): close the AI-simulation subsystem (verbatim)

Copied the 89 uncopied AI*SimulationUtility/extension files defining the
AIVirtualCard/AIVirtualField extension methods; the compile loop then auto-closed
the revealed type deps (~3049 files total, drift-clean). 10.0k -> 62 errors.

SVSim.BattleEngine/Engine/CostHalfRoundDownModifier.cs

@@ -0,0 +1,19 @@
+using System;
+
+public class CostHalfRoundDownModifier : CostHalfModifier
+{
+	public CostHalfRoundDownModifier(bool isResidentModifier)
+		: base(isResidentModifier)
+	{
+	}
+
+	public override int CalcCost(int cost)
+	{
+		return (int)Math.Floor((float)cost / 2f);
+	}
+
+	public override ICardCostModifier Clone()
+	{
+		return new CostHalfRoundDownModifier(base.IsResidentModifier);
+	}
+}