feat: implement cbz writing and pdf reading

tests/pdf_reader_tests.rs

@@ -0,0 +1,51 @@
+use cbz2pdf::formats::pdf::{PdfReader, PdfWriter};
+use cbz2pdf::formats::{FormatReader, FormatWriter};
+use cbz2pdf::model::{Document, ImagePage};
+
+fn make_small_jpeg(w: u32, h: u32, rgb: [u8; 3]) -> (Vec<u8>, image::DynamicImage) {
+    let mut img = image::ImageBuffer::<image::Rgb<u8>, _>::new(w, h);
+    for p in img.pixels_mut() {
+        *p = image::Rgb(rgb);
+    }
+    let dynimg = image::DynamicImage::ImageRgb8(img);
+
+    let mut buf = Vec::new();
+    {
+        let mut cursor = std::io::Cursor::new(&mut buf);
+        let mut enc = image::codecs::jpeg::JpegEncoder::new_with_quality(&mut cursor, 85);
+        let rgb8 = dynimg.to_rgb8();
+        enc.encode(&rgb8, w, h, image::ColorType::Rgb8.into())
+            .unwrap();
+    }
+    (buf, dynimg)
+}
+
+#[test]
+fn pdf_reader_extracts_jpeg_xobject_and_preserves_dct() {
+    // Build a PDF with one JPEG-backed page
+    let (jpeg_dct, dynimg) = make_small_jpeg(3, 2, [10, 20, 30]);
+    let page = ImagePage {
+        name: "p1.jpg".into(),
+        image: dynimg.clone(),
+        jpeg_dct: Some(jpeg_dct.clone()),
+    };
+    let doc = Document::new(vec![page]);
+
+    let temp_dir = tempfile::tempdir().expect("tmpdir");
+    let pdf_path = temp_dir.path().join("in.pdf");
+
+    PdfWriter.write(&doc, &pdf_path).expect("write pdf");
+
+    // Read back with PdfReader
+    let out = PdfReader.read(&pdf_path).expect("read pdf");
+    assert_eq!(out.pages.len(), 1, "should have one page extracted");
+    let p = &out.pages[0];
+    assert_eq!(p.image.width(), dynimg.width());
+    assert_eq!(p.image.height(), dynimg.height());
+    assert!(p.jpeg_dct.is_some(), "should preserve DCT for JPEG images");
+    assert_eq!(
+        p.jpeg_dct.as_ref().unwrap(),
+        &jpeg_dct,
+        "JPEG bytes should match"
+    );
+}