Modernize the uses of raft in cuVS

[achirkin]

A non-breaking src-only changes to modernize the use of raft primitives across cuVS source code. The general rule applied here is to prefer raft helpers taking raft::resources as an argument over other raft helpers over third-party libraries.

• thrust::fill / thrust::fill_n → raft::matrix::fill
• thrust::transform → raft::linalg::map
• thrust::sequence / thrust::tabulate → raft::linalg::map_offset
• raft::linalg::unaryOp / raft::linalg::binaryOp → raft::linalg::map
• raft::linalg::add (pointer-based) → raft::linalg::add (mdspan-based)
• raft::copy (pointer-based) → raft::copy (mdspan-based)
• raft::update_device / raft::update_host → raft::copy (mdspan-based)
• raft::linalg::rowNorm → raft::linalg::norm
• raft::linalg::reduce (pointer-based) → raft::linalg::reduce (mdspan-based)
• cudaMemsetAsync → raft::matrix::fill

The purpose of this PR is to improve the consistency in using the library code (even though sometimes at the cost of a bit more auxiliary code).
This is also a prerequisite to achieving dry run compliance in cuVS if we choose to merge that in rapidsai/raft#2961

[dantegd]

changes look good and comprehensive to me (pending green CI), just found one small place to nitpick :P

[tarang-jain]

Thanks for the meticulous effort! A bunch of comments from my end.

[achirkin]

Thanks @tarang-jain for the suggestions! all addressed

[divyegala]

The FAISS patch should be created in a new file for 26.04.

Not relevant anymore.

[achirkin]

/merge