Function clear_retiring_order_target 

pub fn clear_retiring_order_target(
    state: &mut PortfolioState,
    order_id: &OrderId,
)

Remove order_id from all retiring target sets and direct-retiring set.

O(C) where C = number of in-flight cancel commands (typically 1–3, bounded by the pair-cap batch size). A reverse index would make this O(log C) but adds state complexity for negligible real-world gain.