[dynamo][eval frame] Make CacheEntry a PyObject (#107405)
This PR makes CacheEntry a PyObject. This is prep PR for cache size changes. As CacheEntry is a py object, we can now traverse the linked list in Python and write cache size policies. It was possible to do in C, but Python is just easier to iterate upon. We call convert_frame only when we (re)compile, so a small bump in latency going from C to Python is acceptable here.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107405
Approved by: https://github.com/ezyang
ghstack dependencies: #106917, #107117
