CustomStatePerPawn.cs

// helper class for scribing ref-deep dicts
public class Scribe_Dictionary<T, S>
{
	List<T> tmpKeys;
	List<S> tmpVals;

	public void Scribe(ref Dictionary<T, S> dict, string name)
	{
		if (Verse.Scribe.mode == LoadSaveMode.Saving)
		{
			tmpKeys = new List<T>(dict.Keys);
			tmpVals = new List<S>(dict.Values);
		}

		Scribe_Collections.Look(ref tmpKeys, $"{name}.keys", LookMode.Reference);
		Scribe_Collections.Look(ref tmpVals, $"{name}.vals", LookMode.Deep);

		if (Verse.Scribe.mode == LoadSaveMode.PostLoadInit)
		{
			dict = new Dictionary<T, S>();
			for (var i = 0; i < tmpKeys.Count; i++)
				dict[tmpKeys[i]] = tmpVals[i];
		}
	}
}

// game state
public class GameState : GameComponent
{
	Dictionary<Pawn, State> pawns;
	readonly Scribe_Dictionary<Pawn, State> pawnsHelper;

	public GameState(Game game) : base()
	{
		_ = game;
		pawns = new Dictionary<Pawn, State>();
		pawnsHelper = new Scribe_Dictionary<Pawn, State>();
	}

	public override void ExposeData()
	{
		base.ExposeData();
		pawnsHelper.Scribe(ref pawns, "pawns");
	}

	public static State ForPawn(Pawn pawn)
	{
		var gameState = Current.Game.GetComponent<GameState>();
		if (gameState.pawns.TryGetValue(pawn, out var state) == false)
		{
			state = new State();
			gameState.pawns[pawn] = state;
		}
		return state;
	}
}

// custom state per pawn
public class State : IExposable
{
	public int someValue = 0;

	public void ExposeData()
	{
		Scribe_Values.Look(ref someValue, "someValue", 0);
	}
}