Add support for creating and restoring-from checkpoints

[eyalroz]

With CUDA 12.8, NVIDIA introduced a checkpoint mechanism:

https://docs.nvidia.com/cuda/cuda-driver-api/group__CUDA__CHECKPOINT.html

• cuCheckpointProcessCheckpoint ( int pid, CUcheckpointCheckpointArgs* args )
• cuCheckpointProcessGetRestoreThreadId ( int pid, int* tid )
• cuCheckpointProcessGetState ( int pid, CUprocessState* state )
• cuCheckpointProcessLock ( int pid, CUcheckpointLockArgs* args )
• cuCheckpointProcessRestore ( int pid, CUcheckpointRestoreArgs* args )
• cuCheckpointProcessUnlock ( int pid, CUcheckpointUnlockArgs* args )

Let's support that.