feat(openapi): generate stainless config "more" programmatically (#4164)

Generate the Stainless client config directly from code so we can
validate the config before we ever write the YAML.

This change enforces allowed HTTP verbs/paths, detects duplicate routes
across resources, and ensures README example endpoints exist and match
the OpenAPI spec. The generator now fails fast when config entries
drift, keeping the published config (hopefully) more current with the
spec. I think more validation can be done but this is a good start.

scripts/openapi_generator/__init__.py

@@ -11,6 +11,13 @@ This module provides functionality to generate OpenAPI specifications
 from FastAPI applications.
 """
 
-from .main import generate_openapi_spec, main
-
 __all__ = ["generate_openapi_spec", "main"]
+
+
+def __getattr__(name: str):
+    if name in {"generate_openapi_spec", "main"}:
+        from .main import generate_openapi_spec as _gos
+        from .main import main as _main
+
+        return {"generate_openapi_spec": _gos, "main": _main}[name]
+    raise AttributeError(name)