feat: support cbr reading

tests/cbr_reader_tests.rs

@@ -0,0 +1,23 @@
+use std::fs::File;
+use std::io::Write;
+
+use cbz2pdf::formats::cbr::CbrReader;
+use cbz2pdf::formats::FormatReader;
+
+// We cannot reliably create a RAR archive in tests (tools cannot create .rar),
+// Instead, verify that the reader fails gracefully (returns an error) when given an invalid .cbr
+// file.
+#[test]
+fn cbr_reader_errors_on_invalid_archive() {
+    let temp_dir = tempfile::tempdir().expect("create temp dir");
+    let cbr_path = temp_dir.path().join("invalid.cbr");
+
+    // Write some junk that is definitely not a RAR archive
+    let mut f = File::create(&cbr_path).expect("create cbr");
+    f.write_all(b"this is not a rar archive").unwrap();
+
+    let reader = CbrReader;
+    let res = reader.read(&cbr_path);
+
+    assert!(res.is_err(), "CbrReader should error on invalid archives");
+}