DiT uses scalar twiddle generation instead of the already-written SIMD version

[Shnatsel]

DiF planner will generate the twiddles using a SIMD-accelerated function:

https://github.com/QuState/PhastFT/blob/964dd4cc5cf0672c0373358854ce12259e3beac2/src/planner.rs#L76-L77

But not DiT:

https://github.com/QuState/PhastFT/blob/964dd4cc5cf0672c0373358854ce12259e3beac2/src/planner.rs#L98-L117

[Shnatsel]

We are removing that code in #90 but it can still be salvaged and reused

[Shnatsel]

bfaf84a from #76 shows 10x performance gain in planner creation from this, so this code is worth resurrecting despite the complexity