Add PE_DMA latency-breakdown plots + self-verification harness

scripts/plot_pe_dma_perf.py runs the simulator across six
no-congestion scenarios (SAME_CUBE_PE_LOCAL / REMOTE_BEST /
REMOTE_WORST, REMOTE_CUBE_BEST / REMOTE_WORST, REMOTE_SIP) and
five congestion scenarios (1/2/3 PE hot-target, 8-PE corresp.
cube-to-cube, 8-PE all-hit-pe0). It categorises actual total /
makespan into pe_setup, noc_mesh, ucie, fabric, streaming,
hbm_ctrl, and a contention residual using a wormhole-pipelined
model (first-flit arrival + (n_flits-1)/bottleneck + final
chunk_time).

Outputs:
  docs/diagrams/pe_dma_perf/no_congestion.png — single-PE latency
    by topological distance. Visualises monotonic growth from
    SAME_CUBE_PE_LOCAL (77 ns) up to REMOTE_CUBE_PE_REMOTE_WORST
    (573 ns) and REMOTE_SIP (409 ns).
  docs/diagrams/pe_dma_perf/congestion.png — makespan as concurrent
    issuer count grows. ctrl_hot_{1,2,3}=82/158/230 ns; 8-PE
    eastbound UCIe = 963 ns; 8-PE all-hit-pe0 = 558 ns.
  docs/diagrams/pe_dma_perf/summary.csv — raw rows for re-plotting.

Built-in --verify harness asserts:
  (1) distance monotonicity for no-congestion;
  (2) same-cube paths contain zero UCIe budget;
  (3) remote-cube/SIP paths carry positive UCIe budget;
  (4) breakdown is internally consistent (formula ≤ actual);
  (5) streaming term matches (n_flits-1) × flit_bytes /
      bottleneck_bw within 5 % for the local scenario;
  (6) congestion makespan is monotonic in issuer count;
  (7) 8-PE hotspot strictly exceeds 3-PE hotspot.

Cross-SIP gets a looser 70 % contention slack because the path
crosses two non-flit-aware (pcie_ep) boundaries that force
store-and-forward re-streaming the simple formula does not
attribute. Single-cube scenarios stay under 25 % residual.

All checks PASS at the current model (post ADR-0019 D1/D4
per-PE HBM CTRL restoration).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/diagrams/pe_dma_perf/summary.csv

@@ -0,0 +1,24 @@
+graph,scenario,label,nbytes,n_issuers,total_ns,makespan_ns,min_lat_ns,pe_setup,noc_mesh,ucie,hbm_ctrl,contention,path,first_path
+no_congestion,local,"SAME_CUBE
+PE_LOCAL",16384,,77.0,,,1.0,2.0,0.0,9.0,2.0,pe0.pe_dma -> cube0.r0c0 -> hbm_ctrl.pe0,
+no_congestion,same_cube_best,"SAME_CUBE
+REMOTE_BEST
+(pe0→pe1)",16384,,82.06,,,1.0,5.03,0.0,9.0,4.030000000000001,pe0.pe_dma -> cube0.r0c0 -> cube0.r0c1 -> hbm_ctrl.pe1,
+no_congestion,same_cube_worst,"SAME_CUBE
+REMOTE_WORST
+(pe0→pe7)",16384,,117.50000000000001,,,1.0,26.25,0.0,9.0,18.250000000000014,pe0.pe_dma -> cube0.r0c0 -> cube0.r1c0 -> cube0.r1c1 -> cube0.r1c2 -> cube0.r1c3 -> cube0.r4c3 -> cube0.r4c4 -> cube0.r5c4 -> cube0.r5c5 -> hbm_ctrl.pe7,
+no_congestion,remote_cube_best,"REMOTE_CUBE
+REMOTE_BEST
+(cube0→cube1)",16384,,202.51999999999998,,,1.0,6.0,32.510000000000005,9.0,28.00999999999999,pe0.pe_dma -> cube0.r0c0 -> ucie-N.conn0 -> cube0.ucie-N -> ucie-N.conn3 -> cube0.r0c5 -> ucie-E.conn0 -> cube0.ucie-E -> cube1.ucie-W -> ucie-W.conn0 -> cube1.r0c0 -> hbm_ctrl.pe0,
+no_congestion,remote_cube_worst,"REMOTE_CUBE
+REMOTE_WORST
+(cube0→cube15.pe7)",16384,,573.1199999999999,,,1.0,30.0,219.05999999999995,9.0,188.05999999999995,pe0.pe_dma -> cube0.r0c0 -> ucie-N.conn0 -> cube0.ucie-N -> ucie-N.conn3 -> cube0.r0c5 -> ucie-E.conn0 -> cube0.ucie-E -> cube1.ucie-W -> ucie-W.conn0 -> cube1.r0c0 -> ucie-N.conn0 -> cube1.ucie-N -> ucie-N.conn3 -> cube1.r0c5 -> ucie-E.conn0 -> cube1.ucie-E -> cube2.ucie-W -> ucie-W.conn0 -> cube2.r0c0 -> ucie-N.conn0 -> cube2.ucie-N -> ucie-N.conn3 -> cube2.r0c5 -> ucie-E.conn0 -> cube2.ucie-E -> cube3.ucie-W -> ucie-W.conn0 -> cube3.r0c0 -> ucie-N.conn0 -> cube3.ucie-N -> ucie-N.conn3 -> cube3.r0c5 -> ucie-E.conn0 -> cube3.ucie-E -> ucie-E.conn3 -> cube3.r5c5 -> ucie-S.conn3 -> cube3.ucie-S -> cube7.ucie-N -> ucie-N.conn3 -> cube7.r0c5 -> ucie-E.conn0 -> cube7.ucie-E -> ucie-E.conn3 -> cube7.r5c5 -> ucie-S.conn3 -> cube7.ucie-S -> cube11.ucie-N -> ucie-N.conn3 -> cube11.r0c5 -> ucie-E.conn0 -> cube11.ucie-E -> ucie-E.conn3 -> cube11.r5c5 -> ucie-S.conn3 -> cube11.ucie-S -> cube15.ucie-N -> ucie-N.conn3 -> cube15.r0c5 -> ucie-E.conn0 -> cube15.ucie-E -> ucie-E.conn3 -> cube15.r5c5 -> hbm_ctrl.pe7,
+no_congestion,remote_sip,"REMOTE_SIP
+SAME_CUBE_SAME_PE
+(sip0→sip1)",16384,,408.5216666666663,,,1.0,4.0,37.040000000000006,9.0,209.38499999999962,pe0.pe_dma -> cube0.r0c0 -> ucie-N.conn0 -> cube0.ucie-N -> io0.ucie-P0 -> ucie-P0.conn0 -> io0.noc -> io0.pcie_ep -> fabric.switch0 -> io0.pcie_ep -> io0.noc -> ucie-P0.conn0 -> io0.ucie-P0 -> cube0.ucie-N -> ucie-N.conn0 -> cube0.r0c0 -> hbm_ctrl.pe0,
+congestion,ctrl_hot_1,1×PE → pe0_slice,16384,1,,82.06,82.06,1.0,5.03,0.0,9.0,4.030000000000001,,pe1.pe_dma -> cube0.r0c1 -> cube0.r0c0 -> hbm_ctrl.pe0
+congestion,ctrl_hot_2,2×PE → pe0_slice,16384,2,,158.3450000000001,134.2400000000001,1.0,5.03,0.0,9.0,80.31500000000011,,pe1.pe_dma -> cube0.r0c1 -> cube0.r0c0 -> hbm_ctrl.pe0
+congestion,ctrl_hot_3,3×PE → pe0_slice,16384,3,,230.0750000000001,139.94000000000008,1.0,5.03,0.0,9.0,152.0450000000001,,pe1.pe_dma -> cube0.r0c1 -> cube0.r0c0 -> hbm_ctrl.pe0
+congestion,ucie_eastbound,"8×PE corresp.
+cube0→cube1",16384,8,,962.52,438.52,1.0,6.0,32.510000000000005,9.0,788.01,,pe0.pe_dma -> cube0.r0c0 -> ucie-N.conn0 -> cube0.ucie-N -> ucie-N.conn3 -> cube0.r0c5 -> ucie-E.conn0 -> cube0.ucie-E -> cube1.ucie-W -> ucie-W.conn0 -> cube1.r0c0 -> hbm_ctrl.pe0
+congestion,all_pe_to_pe0,8×PE → pe0_slice,16384,8,,558.2499999999998,195.0,1.0,2.0,0.0,9.0,483.2499999999998,,pe0.pe_dma -> cube0.r0c0 -> hbm_ctrl.pe0