Function player_x_count 

pub fn player_x_count(
    game: &GameState,
    players: &[PlayerId],
    expr: &str,
    source_id: CardId,
    sa: &SpellAbility,
) -> i32

Evaluate player-based X-count expressions. Mirrors Java’s AbilityUtils.playerXCount(List<Player>, String, Card, CardTraitBase).

Sums a property across a list of players. Common properties:

• LifeTotal, Poison, CardsInHand, DomainCount, etc.