Fix Unparsed::encoded_len implementation

`Unparsed` contains raw bytes and as such the length is already stored
inside and doesn't require any additional wrapping.

Additionally fix the `Extension::encoded_len` implementation to use
`Unparsed::encoded_len` instead of directly accessing the `Vec`.

Co-authored-by: Ross Williams <ross@ross-williams.net>
Fixes: #64
Signed-off-by: Wiktor Kwapisiewicz <wiktor@metacode.biz>

Author: wiktor-k

src/proto/message.rs

@@ -617,7 +617,7 @@ impl Decode for Extension {
 
 impl Encode for Extension {
     fn encoded_len(&self) -> ssh_encoding::Result<usize> {
-        [self.name.encoded_len()?, self.details.0.encoded_len()?].checked_sum()
+        [self.name.encoded_len()?, self.details.encoded_len()?].checked_sum()
     }
 
     fn encode(&self, writer: &mut impl Writer) -> ssh_encoding::Result<()> {
@@ -653,7 +653,7 @@ impl From<Vec<u8>> for Unparsed {
 
 impl Encode for Unparsed {
     fn encoded_len(&self) -> ssh_encoding::Result<usize> {
-        self.0.encoded_len()
+        Ok(self.0.len())
     }
 
     fn encode(&self, writer: &mut impl Writer) -> ssh_encoding::Result<()> {