style(lib): address most clippy lints

src/common/buf.rs

@@ -34,10 +34,7 @@ impl<T: Buf> Buf for BufList<T> {
 
     #[inline]
     fn bytes(&self) -> &[u8] {
-        for buf in &self.bufs {
-            return buf.bytes();
-        }
-        &[]
+        self.bufs.front().map(Buf::bytes).unwrap_or_default()
     }
 
     #[inline]

src/common/io/rewind.rs

@@ -58,11 +58,11 @@ where
     ) -> Poll<io::Result<usize>> {
         if let Some(mut prefix) = self.pre.take() {
             // If there are no remaining bytes, let the bytes get dropped.
-            if prefix.len() > 0 {
+            if !prefix.is_empty() {
                 let copy_len = cmp::min(prefix.len(), buf.len());
                 prefix.copy_to_slice(&mut buf[..copy_len]);
                 // Put back whats left
-                if prefix.len() > 0 {
+                if !prefix.is_empty() {
                     self.pre = Some(prefix);
                 }
 

src/common/lazy.rs

@@ -49,9 +49,8 @@ where
     type Output = R::Output;
 
     fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
-        match self.inner {
-            Inner::Fut(ref mut f) => return Pin::new(f).poll(cx),
-            _ => (),
+        if let Inner::Fut(ref mut f) = self.inner {
+            return Pin::new(f).poll(cx);
         }
 
         match mem::replace(&mut self.inner, Inner::Empty) {