Function preprocess_for_rec 

pub fn preprocess_for_rec(
    img: &DynamicImage,
    target_height: u32,
    params: &NormalizeParams,
) -> OcrResult<ArrayBase<OwnedRepr<f32>, Dim<[usize; 4]>>>

Convert image to recognition model input tensor

Output format: [1, 3, H, W] (NCHW) Height is fixed at 48 (or specified value), width scaled proportionally