In #620, we remove Python stubs from this repository and generate them every time to build the doc.
But the API document for qulacs.* submodule is not generated correctly(link).

Before #620, the stubs for a submodule is written in, for example, pysrc/qulacs/circuit/__init__.pyi.
But now ./script/update_stubs.sh(internally stubgen and pybind11-stubgen) generates the stubs in pysrc/qulacs/circuit.pyi, which seems to be ignored by Sphinx(and its plugin).

So we have to

• find any options of stubgen to generate the stubs in pysrc/qulacs/***/__init__.pyi
• rename generated files to desired ones as a workaround