quant ops: Dequantize weight in-place (reduce flux2 VRAM usage) #10935
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In flux2 these weights are huge (200MB). As plain_tensor is a throw-away deep copy, do this multiplication in-place to save VRAM.
This will at least improve (if not fully fix): #10891
Example test conditions:
RTX5090
--reserve-vram 8.9 (to emulate 3090 VRAM ceiling)
Before (peak is 23.3GB):
After (peak is 23.0GB):