Function calculate_measure_along_linestring 

pub fn calculate_measure_along_linestring(
    linestring: &LineString<f64>,
    point: &Point<f64>,
) -> Result<f64, ProjectionError>

Calculate the distance along a linestring from its start to a given point.

Locates the segment closest to point using an equirectangular approximation (cos(lat) scaling), then accumulates haversine distances up to that segment plus the fractional part within it.