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/scripts/update_sdk_artifacts.py

@@ -793,7 +793,7 @@ def _render_thread_block(
         "        input: Input,",
         "        *,",
         *_kw_signature_lines(turn_fields),
-        "    ) -> Turn:",
+        "    ) -> TurnHandle:",
         "        wire_input = _to_wire_input(input)",
         "        params = TurnStartParams(",
         "            thread_id=self.id,",
@@ -801,7 +801,7 @@ def _render_thread_block(
         *_model_arg_lines(turn_fields),
         "        )",
         "        turn = self._client.turn_start(self.id, wire_input, params=params)",
-        "        return Turn(self._client, self.id, turn.turn.id)",
+        "        return TurnHandle(self._client, self.id, turn.turn.id)",
     ]
     return "\n".join(lines)
 
@@ -815,7 +815,7 @@ def _render_async_thread_block(
         "        input: Input,",
         "        *,",
         *_kw_signature_lines(turn_fields),
-        "    ) -> AsyncTurn:",
+        "    ) -> AsyncTurnHandle:",
         "        await self._codex._ensure_initialized()",
         "        wire_input = _to_wire_input(input)",
         "        params = TurnStartParams(",
@@ -828,14 +828,14 @@ def _render_async_thread_block(
         "            wire_input,",
         "            params=params,",
         "        )",
-        "        return AsyncTurn(self._codex, self.id, turn.turn.id)",
+        "        return AsyncTurnHandle(self._codex, self.id, turn.turn.id)",
     ]
     return "\n".join(lines)
 
 
 def generate_public_api_flat_methods() -> None:
     src_dir = sdk_root() / "src"
-    public_api_path = src_dir / "codex_app_server" / "public_api.py"
+    public_api_path = src_dir / "codex_app_server" / "api.py"
     if not public_api_path.exists():
         # PR2 can run codegen before the ergonomic public API layer is added.
         return