analytical-viz: partial batch (B) scaffold — TopologyConfig field + KV / early stages

WIP toward batch-size support. This first commit is behavior-preserving
at the default B=1 (every new multiplication is by max(1, cfg.topo.b) =
1 today) so all existing tests pass. Follow-up commits will:
  - scale the remaining stages (S6/S7/S8/S9/S10 + C1/C2/C3 + FFN + FFN AR)
  - add a batch selectbox to the sidebar
  - forward b through auto_suggest / auto_explore / auto_hardware

Changes so far:
  - TopologyConfig: new b: int = 1 field (batch size).
  - memory_layout.per_pe_kv_cache_bytes: * B (each concurrent request
    keeps its own KV cache slice).
  - stage_rmsnorm / stage_wq / stage_wkv / stage_kv_append /
    _per_hop_qkT_pv: FLOPs and activation memory scaled by B; weight
    bytes stay fixed (weights shared across the batch).

Verified: 24 pytest tests still pass at default B=1.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/analytical_visualization/memory_layout.py

@@ -74,17 +74,19 @@ def per_pe_kv_cache_bytes(cfg: FullConfig) -> int:
       TP > H_kv, each KV head is duplicated across TP/H_kv ranks so
       per-PE storage doesn't shrink below 1 head.
     - PP: only layers_per_stage layers stored per PE.
+    - Batch (B): each concurrent request keeps its own KV cache slice.
     """
     m = cfg.model
     pp = cfg.topo.pp
     tp = cfg.topo.tp
+    B = max(1, cfg.topo.b)
     if cfg.topo.kv_shard_mode == "replicate":
         hkv_per_pe_bytes = max(1.0, m.h_kv / tp)
     else:
         hkv_per_pe_bytes = m.h_kv / tp
     layers_per_stage = (m.layers + pp - 1) // pp
     per_layer = 2 * cfg.topo.s_local * hkv_per_pe_bytes * m.d_head * m.bytes_per_elem
-    return int(per_layer * layers_per_stage)
+    return int(per_layer * layers_per_stage * B)
 
 
 def per_pe_transient_bytes(cfg: FullConfig) -> int: