1. grouped_linear.py: Pre-allocate _scale_a_buf for swizzle
- Same fix as linear.py — avoids torch.zeros per call
- Uses correctly-sized view for pad_and_swizzle_single
2. quantize.py: Replace torch.zeros_like with scalar 0.0
- torch.zeros_like allocates a full tensor every call
- torch.where(cond, 0.0, x) broadcasts scalar — no allocation