Function parse_ws_spot_index_price_update 

pub fn parse_ws_spot_index_price_update(
    stats: &LighterSpotMarketStats,
    instrument: &InstrumentAny,
    timestamp_ms: u64,
    ts_init: UnixNanos,
) -> Result<IndexPriceUpdate>

Parses a Lighter spot market-stat update into an index price update.

Errors

Returns an error if the index price or timestamp cannot be converted.