docs: Fix missing docstring and implement cat and size methods

Co-authored-by: aider (openai/andrew/openrouter/sonoma-sky-alpha) <aider@aider.chat>

src/compression_engine.rs

@@ -155,4 +155,57 @@ pub trait CompressionEngine {
     ///
     /// # Returns
     ///
-    /// * `Result<()>` - Success if
+    /// * `Result<()>` - Success if the content is output, or an error.
+    ///
+    /// # Errors
+    ///
+    /// Propagates errors from copying to stdout.
+    fn cat(&self, file_path: PathBuf) -> Result<()> {
+        let mut stdout = io::stdout().lock();
+        self.copy(file_path, &mut stdout)
+    }
+
+    /// Calculates the decompressed size of a file.
+    ///
+    /// Reads the entire decompressed content to determine its size in bytes.
+    ///
+    /// # Arguments
+    ///
+    /// * `file_path` - Path to the compressed file.
+    ///
+    /// # Returns
+    ///
+    /// * `Result<usize>` - The decompressed size in bytes, or an error.
+    ///
+    /// # Errors
+    ///
+    /// Returns an error if the file cannot be opened or read.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let engine = /* some engine */;
+    /// let size = engine.size("file.gz".into()).unwrap();
+    /// println!("Decompressed size: {} bytes", size);
+    /// ```
+    fn size(&self, file_path: PathBuf) -> Result<usize> {
+        let mut reader = self.open(file_path)?;
+        let mut buffer = [0; libc::BUFSIZ as usize];
+        let mut size: usize = 0;
+
+        loop {
+            let n = reader.read(&mut buffer[..libc::BUFSIZ as usize])?;
+            if n == 0 {
+                debug!("COMPRESSION: EOF");
+                break;
+            }
+
+            size += n;
+        }
+
+        Ok(size)
+    }
+}
+
+lazy_static! {
+    /// Mapping of