Rewrite SamplerSPEED to match official speed/comfyui, update README with flux preset results and attribution
- Rewrite speed_sampler.py: hard DCT truncation, DCT/DWT/FFT support,
delta_optimal + manual modes, per-transition seed offset, single-sigma
patching, flux/wan21 presets
- Add spectral_utils.py: faithful extraction of paper's Eq. 5/6/9/10 and
spectral expansion from official speed/utils.py
- Update README with flux preset results (20s), new input docs, remove
old acidmiku/vibecoded notes
- Add attribution to each Python file: https://github.com/howardhx/speed
- 23 tests passing for spectral_utils.py