Function parse_gnss_csv_str 

pub fn parse_gnss_csv_str(
    csv_text: &str,
    crs: &str,
    lat_col: &str,
    lon_col: &str,
    time_col: &str,
) -> Result<Vec<GnssPosition>, ProjectionError>

In-memory variant of parse_gnss_csv that accepts the full CSV text directly. No disk I/O is performed; required by the .NET bindings for database-backed callers (FR-012).