Function parse_betfair_starting_prices 

pub fn parse_betfair_starting_prices(
    market_id: &str,
    def: &MarketDefinition,
    ts_event: UnixNanos,
    ts_init: UnixNanos,
) -> Vec<BetfairStartingPrice>

Extracts BetfairStartingPrice values from a market definition’s runners.

Returns one entry per runner that has a non-None BSP value.