The package we were using was only for Python 3.4 and didn't include
async/await which broke imports in any script that used async/await.
Fixes: https://github.com/pybricks/support/issues/873
This replaces the Python parsing library. The python-ast package has
really poor performance (many seconds to parse a 500 line file). The
new package can parse a file about 100 times faster.