chore: apply beta clippy fixes

Author: link2xt

src/error.rs

@@ -103,6 +103,6 @@ mod test {
                 "For explanation visit https://www.gmx.net/mail/senderguidelines?c=bl".to_string(),
             ],
         ));
-        assert_eq!(format!("{}", err), "permanent: gmx.net (mxgmx117) Nemesis ESMTP Service not available; No SMTP service; IP address is block listed.; For explanation visit https://www.gmx.net/mail/senderguidelines?c=bl".to_string());
+        assert_eq!(format!("{err}"), "permanent: gmx.net (mxgmx117) Nemesis ESMTP Service not available; No SMTP service; IP address is block listed.; For explanation visit https://www.gmx.net/mail/senderguidelines?c=bl".to_string());
     }
 }

src/response.rs

@@ -336,7 +336,7 @@ mod test {
         let res = parse_response(raw_response);
         match res {
             Err(nom::Err::Incomplete(_)) => {}
-            _ => panic!("Expected incomplete response, got {:?}", res),
+            _ => panic!("Expected incomplete response, got {res:?}"),
         }
     }
 

src/stream.rs

@@ -95,7 +95,7 @@ impl<S: BufRead + Write + Unpin> SmtpStream<S> {
             }
         }
 
-        Err(std::io::Error::new(std::io::ErrorKind::Other, "incomplete").into())
+        Err(std::io::Error::other("incomplete").into())
     }
 
     /// Sends the message content.