Add GPU driver and CUDA version to metrics

[pmady]

Currently the Metrics struct doesn't include the NVIDIA driver version or CUDA version. These are useful for agents diagnosing compatibility issues.

What to do:

• Add DriverVersion and CUDAVersion fields to the Metrics struct in gpu/gpu.go
• Populate them in gpu/nvml.go using nvml.SystemGetDriverVersion() and nvml.SystemGetCudaDriverVersion()
• Update the mock with sample values
• Update tests

Files to edit: gpu/gpu.go, gpu/nvml.go, gpu/mock.go, server/server_test.go

[pavsorab]

@pmady can you assign this to me ?