Add `impureWithCuda` dev shell (#2677)
* Add `impureWithCuda` dev shell
This shell is handy when developing some kernels jointly with TGI - it
adds nvcc and a bunch of commonly-used CUDA libraries to the environment.
We don't add this to the normal impure shell to keep the development
environment as clean as possible (avoid accidental dependencies, etc.).
* Add cuDNN
