Function sounding_analysis::cold_surface_temperature_layer

pub fn cold_surface_temperature_layer(
    snd: &Sounding, 
    warm_layers: &[Layer]
) -> Result<Option<Layer>>

Assuming a warm layer aloft given by warm_layers, measure the cold surface layer. If there are no warm layers aloft, return None since cold surface layer extends the full depth of the atmosphere and is irrelevant.