[breaking change] Update edition from 2018 to 2021

And fix clippy warnings

src/blob/mod.rs

@@ -274,7 +274,6 @@ impl Blob<'_> {
     #[inline]
     #[must_use]
     pub fn len(&self) -> usize {
-        use std::convert::TryInto;
         self.size().try_into().unwrap()
     }
 

src/blob/pos_io.rs

@@ -265,7 +265,7 @@ mod test {
         ));
         blob.raw_read_at_exact(&mut s2, 5).unwrap_err();
 
-        let end_pos = blob.seek(std::io::SeekFrom::Current(0)).unwrap();
+        let end_pos = blob.stream_position().unwrap();
         assert_eq!(end_pos, 1);
         Ok(())
     }