Publish GPU package

[ikanago]

Currently, we do not publish qulacs Python package for GPU.
So we build GPU package in CI and publish it (we do not need GPU environment for build).

[ikanago]

Since we are to publish multiple packages from one repository, we cannot build them with current settings.
We have to select one of these options:

• Split directories for each packages and place pyproject.toml in each of them
• Way back to setup.py to build packages with different name dynamically
• Merge CPU and GPU package. CPU users and GPU users use the same package
  • CPU users can be influenced by the behavior of GPU code

[ikanago]

@ qulacs community,
If there are some people who needs GPU package, we will work on the problem.
I would be glad if you tell your needs below!

[BrunoLiegiBastonLiegi]

Hello, we are in the process of implementing a qulacs backend in qibo. As the plan is to have qulacs-gpu as an optional dependency, we would need the GPU package I believe.

[ikanago]

Memo: pennylane's qulacs plugin needs GPU package
PennyLaneAI/pennylane-qulacs#63