GitLab

* add cuda source

* moving codes from kernel2 branch

* operator overloading

* Better error message for unsupported device

* fix c tests

* coo sort using cusparse

* move test_rpc to distributed

* lint

* address comments and add utests
Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>
Co-authored-by: Chao Ma <mctt90@gmail.com>
Co-authored-by: xiang song(charlie.song) <classicxsong@gmail.com>