frontend keeps loading

The `GET /object_info` endpoint performs synchronous, blocking computation inside an async route handler. On instances with a large number of custom nodes installed it takes enumerous time. I temporarily hack this by pre-generating a static JSON cache of the object_info response at startup, then serving that file directly from the endpoint.

https://github.com/Comfy-Org/ComfyUI/blob/63d1bbdb407c69370d407ce5ced6ca3f917528a8/server.py#L705

related issues: #7329 #5219