Function adaptive_threshold_gradient_window 

pub fn adaptive_threshold_gradient_window(
    img: &ImageView<'_>,
    gradient_map: &[u8],
    integral: &[u64],
    output: &mut [u8],
    min_radius: usize,
    max_radius: usize,
    gradient_threshold: u8,
    c: i16,
)

Apply per-pixel adaptive threshold with gradient-based window sizing.

Highly optimized using Parallel processing, precomputed LUTs, and branchless logic.