Previously the error report would have all sections glued together:
- The assertion representation
- The error explanation
- The full diff
This makes it hard to see at a glance where which one starts and ends.
One of the representation (dataclasses, tuples, attrs) does display a
newlines at the start already.
Let's add a newlines before the error explanation and before the full
diff, so we get an easier to read report.
This has one disadvantage: we get one line less in the least verbose
mode, where the output gets truncated.