Enable the creation of streams with variable execution priority

[kris-rowe]

Details

• All of the programming models used to implement the various OCCA backends now support some form of priority streams/queues.
• This feature is partially implemented, currently only for CUDA mode. (Update CUDA backend to create streams with priority #773)

References

• CUDA Driver: cuStreamCreateWithPriority
• HIP: hipStreamCreateWithPriority
• SYCL: oneAPI queue priority extension
• OpenCL: Khronos queue priority extension