chore(phase6,bench): record quantization tradeoff matrix
Phase 6 reference numbers for SD1.5 1x512x512 SPLIT_EINSUM, captured
against commit 0bbd8d8 on M2 Pro 32GB (macOS 26.1, coremltools 9.0,
numpy 1.26.4, torch 2.7.1, Python 3.12.11) — same toolchain as Phase 5
baseline ef2a18c-rebased 1e5791d.
Headline:
- size shrinks 1641 MB -> 822 / 617 / 412 MB (1/2, 1/2.7, 1/4)
- fwd-pass median drops 197 ms -> 187 / 183 / 180 ms (5-9% faster)
- noise_pred PSNR vs unquantized: 53.5 / 40.2 / 27.5 dB
The fwd-ms improvement is mostly weight-load bandwidth (smaller LUT
reads). PSNR is on the raw UNet output at a fixed seed; final-image
PSNR after 20 sampler steps is comfortably higher.
aszc-dev
3adb216763