Function extract_param 

fn extract_param(
    args: &[RValue],
    named: &[(String, RValue)],
    name: &str,
    positional_index: usize,
    default: f64,
) -> f64

Extract an optional f64 parameter from named args or positional index.

Checks named args first (handles gap cases where the arg was named but earlier formals were omitted), then falls back to positional index.