Add SchedulerV2 (pe_accel), DPPolicy overrides, and new benchmarks

- Add cycle-accurate PE accelerator scheduler (SchedulerV2) with tiled
  GEMM/Math pipelines (DMA_IN → GEMM → MATH → DMA_WB)
- Add DPPolicy num_pes/num_cubes/num_sips overrides for single-PE testing
- Support tuple target_pe for targeting specific PE subsets
- Add gemm_single_pe and gpt3_qkv benchmarks
- Switch default topology to pe_scheduler_v2

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/kernbench/policy/placement/dp.py

@@ -13,11 +13,19 @@ class DPPolicy:
       - "replicate": full copy at each unit
       - "column_wise": split K (column) axis across units
       - "row_wise": split M (row) axis across units
+
+    Optional overrides (default None = use topology dimensions):
+      - num_pes: override PEs per cube (e.g., 1 for single-PE test)
+      - num_cubes: override cubes per SIP (e.g., 1 for single-cube test)
+      - num_sips: override SIP count
     """
 
     sip: Literal["replicate", "column_wise", "row_wise"] = "replicate"
     cube: Literal["replicate", "column_wise", "row_wise"] = "replicate"
     pe: Literal["replicate", "column_wise", "row_wise"] = "replicate"
+    num_pes: int | None = None
+    num_cubes: int | None = None
+    num_sips: int | None = None
 
 
 def _split_shape(