Add Python SDK public API and examples (#14446)

## TL;DR
WIP esp the examples

Thin the Python SDK public surface so the wrapper layer returns
canonical app-server generated models directly.

- keeps `Codex` / `AsyncCodex` / `Thread` / `Turn` and input helpers,
but removes alias-only type layers and custom result models
- `metadata` now returns `InitializeResponse` and `run()` returns the
generated app-server `Turn`
- updates docs, examples, notebook, and tests to use canonical generated
types and regenerates `v2_all.py` against current schema
- keeps the pinned runtime-package integration flow and real integration
coverage

  ## Validation
  - `PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests`
- `GH_TOKEN="$(gh auth token)" RUN_REAL_CODEX_TESTS=1
PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests -rs`

---------

Co-authored-by: Codex <noreply@openai.com>

sdk/python/examples/03_turn_stream_events/sync.py

@@ -0,0 +1,55 @@
+import sys
+from pathlib import Path
+
+_EXAMPLES_ROOT = Path(__file__).resolve().parents[1]
+if str(_EXAMPLES_ROOT) not in sys.path:
+    sys.path.insert(0, str(_EXAMPLES_ROOT))
+
+from _bootstrap import (
+    assistant_text_from_turn,
+    ensure_local_sdk_src,
+    find_turn_by_id,
+    runtime_config,
+)
+
+ensure_local_sdk_src()
+
+from codex_app_server import Codex, TextInput
+
+with Codex(config=runtime_config()) as codex:
+    thread = codex.thread_start(model="gpt-5.4", config={"model_reasoning_effort": "high"})
+    turn = thread.turn(TextInput("Explain SIMD in 3 short bullets."))
+
+    event_count = 0
+    saw_started = False
+    saw_delta = False
+    completed_status = "unknown"
+
+    for event in turn.stream():
+        event_count += 1
+        if event.method == "turn/started":
+            saw_started = True
+            print("stream.started")
+            continue
+        if event.method == "item/agentMessage/delta":
+            delta = getattr(event.payload, "delta", "")
+            if delta:
+                if not saw_delta:
+                    print("assistant> ", end="", flush=True)
+                print(delta, end="", flush=True)
+                saw_delta = True
+            continue
+        if event.method == "turn/completed":
+            completed_status = getattr(event.payload.turn.status, "value", str(event.payload.turn.status))
+
+    if saw_delta:
+        print()
+    else:
+        persisted = thread.read(include_turns=True)
+        persisted_turn = find_turn_by_id(persisted.thread.turns, turn.id)
+        final_text = assistant_text_from_turn(persisted_turn).strip() or "[no assistant text]"
+        print("assistant>", final_text)
+
+    print("stream.started.seen:", saw_started)
+    print("stream.completed:", completed_status)
+    print("events.count:", event_count)