perf(util): optimize <BufList as Buf>::has_remaining (#94)

This returns true much faster than summing _all_ bufs in the list.

Author: tesaguri

http-body-util/src/util.rs

@@ -27,6 +27,11 @@ impl<T: Buf> Buf for BufList<T> {
         self.bufs.iter().map(|buf| buf.remaining()).sum()
     }
 
+    #[inline]
+    fn has_remaining(&self) -> bool {
+        self.bufs.iter().any(|buf| buf.has_remaining())
+    }
+
     #[inline]
     fn chunk(&self) -> &[u8] {
         self.bufs.front().map(Buf::chunk).unwrap_or_default()