Add Python app-server SDK (#14435)

## TL;DR
Bring the Python app-server SDK from `main-with-prs-13953-and-14232`
onto current `main` as a standalone SDK-only PR.

- adds the new `sdk/python` and `sdk/python-runtime` package trees
- keeps the scope to the SDK payload only, without the unrelated
branch-history or workflow changes from the source branch
- regenerates `sdk/python/src/codex_app_server/generated/v2_all.py`
against current `main` schema so the extracted SDK matches today's
protocol definitions

## Validation
- `PYTHONPATH=sdk/python/src python3 -m pytest sdk/python/tests`

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

sdk/python-runtime/src/codex_cli_bin/__init__.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+PACKAGE_NAME = "codex-cli-bin"
+
+
+def bundled_codex_path() -> Path:
+    exe = "codex.exe" if os.name == "nt" else "codex"
+    path = Path(__file__).resolve().parent / "bin" / exe
+    if not path.is_file():
+        raise FileNotFoundError(
+            f"{PACKAGE_NAME} is installed but missing its packaged codex binary at {path}"
+        )
+    return path
+
+
+__all__ = ["PACKAGE_NAME", "bundled_codex_path"]