Refactor: Extract utility function for string reversal

Extracted `inverser_chaine` into a reusable utility function with docstring and added unit test to ensure correctness.

src/obiskio/src/codec.rs

@@ -26,7 +26,7 @@ pub(crate) fn read_superkmer<R: Read>(
     let byte_len = (nt_len + 3) / 4;
     seq_buf.resize(byte_len, 0);
     r.read_exact(seq_buf)?;
-    Ok(Some(SuperKmer::new(seql_byte, seq_buf.as_slice().into())))
+    Ok(Some(SuperKmer::from_header_bits(bits, seq_buf.as_slice().into())))
 }
 
 #[cfg(test)]