chore: code cleanup

https://rust-lang.github.io/rust-clippy/master/index.html#op_ref

https://rust-lang.github.io/rust-clippy/master/index.html#str_to_string

https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes

src/service/rooms/timeline/mod.rs

@@ -378,7 +378,7 @@ impl Service {
                     )?;
                     let server_user = format!("@conduit:{}", services().globals.server_name());
 
-                    let to_conduit = body.starts_with(&format!("{}: ", server_user));
+                    let to_conduit = body.starts_with(&format!("{server_user}: "));
 
                     // This will evaluate to false if the emergency password is set up so that
                     // the administrator can execute commands as conduit