The purpose of using cusolver*Host

[Fengzch]

Hello, regarding the v26.02.00a branch, in the file raft/cpp/include/raft/spectral/detail/lapack.hpp, why were cusolver*Host interfaces used? What was the purpose of doing this, and why weren't the corresponding device interfaces used instead?
Furthermore, since these interfaces are not publicly exposed, how can I obtain relevant documentation for them?