[Edge][WP2] Add initialization timeline and cold-start profiler

* vllm_omni/engine/init_timeline.py: InitTimeline phase collector; engine
  phases (stages_init, g3_device_lock, g2_spawn/ready) and worker phases
  (proc_entry, engine_core_init, init_device, load_model/load_weights,
  talker_mtp_init, attn_prewarm, cudagraph_capture, talker_mtp_capture,
  code2wav_cudagraph, predictor_setup_compile/warmup/cudagraph) recorded via
  worker_phase/timed_phase; workers append JSONL under
  VLLM_OMNI_INIT_TIMELINE_DIR (inherited at spawn) and the engine merges them.
  Enabled by VLLM_OMNI_INIT_TIMELINE=<json> or log_stats; table logged at INFO,
  partial table on orchestrator startup timeout, suggested timeouts logged.
* omni_base.py: named deploy profiles default to stage_init_timeout=900 /
  init_timeout=1500 unless given explicitly.
* gpu_model_runner._init_talker_mtp tolerates max_cudagraph_capture_size=None;
  gpu_ar_model_runner.shutdown skips CUDA graph teardown on CPU.
* benchmarks/tts/init_profile.py: runs stream_latency_bench --init-only per
  configuration (default, cold_cache, eager_stage1, eager_both,
  parallel_stage_init, edge, ...) and tabulates phase durations.
* stream_latency_bench: --parallel-stage-init / --deploy-profile flags; the
  resource poller no longer shadows Thread._stop and skips GPU sampling on CPU.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/benchmarks/test_init_profile.py

@@ -0,0 +1,60 @@
+"""Tests for benchmarks/tts/init_profile.py helpers (CPU)."""
+
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+import pytest
+import yaml
+
+sys.path.insert(0, str(Path(__file__).parent.parent.parent / "benchmarks" / "tts"))
+import init_profile as ip  # noqa: E402
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+
+def test_flatten_edge_yaml_inherits_base_and_applies_updates(tmp_path):
+    edge = ip.DEPLOY_DIR / "edge" / "qwen3_tts.yaml"
+    flat = ip._flatten_deploy_yaml(edge)
+    assert "base_config" not in flat
+    assert [s["stage_id"] for s in flat["stages"]] == [0, 1]
+    # inherited from base
+    assert flat["stages"][0]["trust_remote_code"] is True
+    # overridden by edge
+    assert flat["stages"][0]["max_num_seqs"] == 4
+    assert flat["connectors"]["connector_of_shared_memory"]["extra"]["codec_chunk_ramp"] == [2, 4, 8, 16, 25]
+
+    out = ip.write_variant_yaml(
+        edge, {"stages": {1: {"enforce_eager": True}}, "top": {"async_chunk": False}}, tmp_path, "v"
+    )
+    doc = yaml.safe_load(out.read_text())
+    assert doc["stages"][1]["enforce_eager"] is True
+    assert doc["stages"][0].get("enforce_eager") is None
+    assert doc["async_chunk"] is False
+
+
+def test_phase_durations_and_table():
+    timeline = {
+        "total_s": 100.0,
+        "phases": [
+            {"name": "load_weights", "dur_s": 10.0, "stage_id": 0},
+            {"name": "load_weights", "dur_s": 5.0, "stage_id": 1},
+            {"name": "predictor_setup_compile", "dur_s": 40.0, "stage_id": 0},
+        ],
+    }
+    d = ip.phase_durations(timeline)
+    assert d == {"load_weights": 15.0, "predictor_setup_compile": 40.0}
+    by_stage = ip.phase_durations_by_stage(timeline)
+    assert by_stage["0"]["load_weights"] == 10.0 and by_stage["1"]["load_weights"] == 5.0
+    table = ip.render_table([{"config": "default", "init_s": 100.0, "ttfa_ms": 30.0, "gpu_mib": 5000, "phases": d}])
+    assert "| default | 100.0 | 30.0 | 5000 |" in table
+    assert "predictor_setup_compile" in table.splitlines()[0]
+    assert ip.phase_durations(None) == {}
+
+
+def test_config_registry_names():
+    for name in ("default", "cold_cache", "eager_stage1", "eager_both", "parallel_stage_init", "edge"):
+        assert name in ip.CONFIGS
+    assert ip.CONFIGS["cold_cache"].fresh_caches is True
+    assert ip.CONFIGS["parallel_stage_init"].extra_args == ["--parallel-stage-init"]