CUDA kernels names shouldn't all be "kernel"

[torsteingrindvik]

Hardcoded here:

1. https://github.com/tracel-ai/cubecl/blob/main/crates/cubecl-cuda/src/compute/server.rs#L366
2. https://github.com/tracel-ai/cubecl/blob/main/crates/cubecl-cpp/src/shared/kernel.rs#L125

I think that perhaps either

1. The kernel name should always be equal to the Rust name, or
2. It should default to the Rust name but let the user name it via some API or via the proc macro (e.g. #[cube(launch, name = "foo")]

The reason for having names is that if profiling with Nsight tools we can see which kernels are which. This is diffifcult when the names are the same.