This commit integrates the GPU-based channel simulation pipeline into
the ulsim.
A `--cuda` command-line flag is added to enable the GPU path at
runtime. When activated, the simulator will:
- Allocate all necessary GPU and pinned host memory via the
`init_cuda_chsim_buffers` helper function.
- In the main simulation loop, call the `run_channel_pipeline_cuda`
function to perform the channel simulation on the GPU, bypassing the
CPU-based functions.
- Clean up all CUDA resources on exit using the
`free_cuda_chsim_buffers` helper.
The cpu path is also updated to use multipath_channel_float and add_noise_float.
Nika Ghaderi
afc52abb8a