test(03-01): add 19 unit tests for crypto, compression, and format modules

- crypto: encrypt/decrypt roundtrip, empty data, size formula, HMAC compute/verify, SHA-256 known values
- compression: compress/decompress roundtrip, empty data, large data, should_compress heuristic
- format: header write/read roundtrip, TOC entry roundtrip (ASCII + Cyrillic + empty name), bad magic/version rejection, entry size calculation matching FORMAT.md worked example
- Update hex-literal to v1.1

src/compression.rs

@@ -49,3 +49,51 @@ pub fn should_compress(filename: &str, no_compress_list: &[String]) -> bool {
             | "7z" | "rar" | "jar"
     )
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_compress_decompress_roundtrip() {
+        let data = b"Hello, World! This is test data for compression.";
+        let compressed = compress(data).unwrap();
+        let decompressed = decompress(&compressed).unwrap();
+        assert_eq!(decompressed, data);
+    }
+
+    #[test]
+    fn test_compress_decompress_empty() {
+        let data = b"";
+        let compressed = compress(data).unwrap();
+        let decompressed = decompress(&compressed).unwrap();
+        assert_eq!(decompressed, data.as_slice());
+    }
+
+    #[test]
+    fn test_compress_decompress_large() {
+        // 10000 bytes of pattern data
+        let data: Vec<u8> = (0..10000).map(|i| (i % 256) as u8).collect();
+        let compressed = compress(&data).unwrap();
+        let decompressed = decompress(&compressed).unwrap();
+        assert_eq!(decompressed, data);
+    }
+
+    #[test]
+    fn test_should_compress_text() {
+        assert!(should_compress("readme.txt", &[]));
+        assert!(should_compress("data.json", &[]));
+    }
+
+    #[test]
+    fn test_should_not_compress_known_extensions() {
+        assert!(!should_compress("app.apk", &[]));
+        assert!(!should_compress("photo.jpg", &[]));
+        assert!(!should_compress("archive.zip", &[]));
+    }
+
+    #[test]
+    fn test_should_not_compress_excluded() {
+        assert!(!should_compress("special.dat", &["special.dat".into()]));
+    }
+}