fn category_members(
spells: &[SpellData],
category: impl Fn(&SpellData) -> Option<CooldownCategoryId>,
) -> PoolIndex<CooldownCategoryId, LocalSpellIdx>fn category_members(
spells: &[SpellData],
category: impl Fn(&SpellData) -> Option<CooldownCategoryId>,
) -> PoolIndex<CooldownCategoryId, LocalSpellIdx>