fix: implement Write trait for digest engines

src/digest_engine/none.rs

@@ -14,11 +14,31 @@ impl DigestEngineNone {
 
 impl DigestEngine for DigestEngineNone {
     fn create(&self) -> Result<Box<dyn Write>> {
-        Ok(Box::new(Self::new()))
+        Ok(Box::new(DummyWriter::new()))
     }
+    
     fn finalize(&mut self) -> io::Result<String> {
         Ok("none".to_string())
     }
     
     fn update(&mut self, _data: &[u8]) {}
 }
+
+// Dummy writer that implements Write for the none digest engine
+struct DummyWriter;
+
+impl DummyWriter {
+    fn new() -> Self {
+        DummyWriter
+    }
+}
+
+impl Write for DummyWriter {
+    fn write(&mut self, _buf: &[u8]) -> io::Result<usize> {
+        Ok(0)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        Ok(())
+    }
+}