As in the [lymph](https://github.com/lycosystem/lymph) repo, we should switch to the `src` layout here, too. Some reasons are provided e.g. [here](https://packaging.python.org/en/latest/discussions/src-layout-vs-flat-layout/).
As in the lymph repo, we should switch to the
srclayout here, too. Some reasons are provided e.g. here.