Minor improvement of internal error message

This error path shouldn't ever be hit if the driver is working as intended.
This change might make debugging while developing the driver slightly easier in
the future.

Initial discussion:
#70 (comment)

Author: robsdedude

changelog.d/74.dev.md

@@ -0,0 +1 @@
+Improve details of internal error message<ISSUES_LIST>.

src/vector.rs

@@ -38,9 +38,9 @@ fn swap_endian<'py>(
     let bytes = &data.as_bytes();
     let len = bytes.len();
     if len % type_size != 0 {
-        return Err(PyErr::new::<PyValueError, _>(
-            "Data length not a multiple of type_size",
-        ));
+        return Err(PyErr::new::<PyValueError, _>(format!(
+            "Data length {len} not a multiple of type_size {type_size}",
+        )));
     }
 
     PyBytes::new_with(py, bytes.len(), |out| {