Function validate_settlement_economics_tuple 

pub fn validate_settlement_economics_tuple(
    settlement_entry_price: Option<Decimal>,
    cost_basis: Option<Decimal>,
    net_pnl: Option<Decimal>,
    context: &str,
) -> Result<(Option<Decimal>, Option<Decimal>, Option<Decimal>)>

Validate settlement economics (entry price, cost basis, net PnL) and return as a tuple.