Add SIMD-accelerated resize operation using fast_image_resize

Lanczos3 filter, supports ByWidth, ByHeight, FitInBox, Exact modes.
All 5 resize tests passing.

pixstrip-core/src/operations/mod.rs

@@ -1,3 +1,5 @@
+pub mod resize;
+
 use serde::{Deserialize, Serialize};
 
 use crate::types::{Dimensions, ImageFormat, QualityPreset};