Update base for Update on "Add quantized input support to cpu_sdpa"

cpu_sdpa (unfused SDPA) previously only supported float inputs.
When the model uses quantized Q/K/V (int8 with per-channel scales
and zero_points), decode fell back to cpu_flash_attention, missing
the ~25-30% throughput improvement from unfused SDPA.

This adds quantized support to cpu_sdpa by:
- Accepting optional quantization params (zero_points, scales for Q/K/V)
- Using _q_at_k_gemm for QK^T (handles both int8 and float)
- Using _qk_at_v_gemm for scoresV (handles both int8 and float)
- Applying scaling factor separately (fused with mask add or max reduction)
- Allocating a dequantization buffer for V when quantized

The dispatch in op_sdpa.cpp is updated to route quantized decode
(seq_len==1) through cpu_sdpa instead of cpu_flash_attention.

Differential Revision: [D96044310](https://our.internmc.facebook.com/intern/diff/D96044310/)

[ghstack-poisoned]

Author: kimishpatel