Investigate how Coconut currently outputs MyPy results and trace the line number mapping. Look at files like `coconut/compiler.py` or `coconut/mypy.py` to understand the existing output formatting. The goal is to prepend the original Coconut line number to the Python line number in the MyPy error messages. Check the comments in issue #332 for any previous attempts or discussions. Implement a mapping that translates the compiled Python line numbers back to the source Coconut line numbers.
