[DFT] cuFFT FORWARD/BACKWARD_SCALE

[FMarno]

Summary

FORWARD/BACKWARD_SCALE not equal to 1.0 should be implemented for the cuFFT backend of the DFT interface.

Problem statement

When #284 is merged, using a FORWARD/BACKWARD_SCALE != 1.0 will result in a oneapi::mkl::unimplemented exception at commit time.

Preferred solution

This could be implemented by queuing another kernel to do the multiplication after the transform is complete.

[FMarno]

Intel/Codeplay currently have no plans to develop this feature