Cache Set/Get __del__ only clears the last video namespace #2846

Repro (current main)

cache_set/v1.py and cache_get/v1.py store a process-global map in WorkflowMemoryCache keyed by video_metadata.video_identifier. Cleanup is __del__ and only remembers self.namespace, which run() overwrites every call:

# cache_set/v1.py on main
def __del__(self):
    if self.namespace:
        WorkflowMemoryCache.clear_namespace(self.namespace)

# run():
self.namespace = namespace  # last video wins

Sequence: set on vidA, then vidB, then the block is destroyed → vidA stays in WorkflowMemoryCache.cache for the process lifetime.

Confirmed by reading origin/main (self.namespace = namespace + __del__ clears only that one).

Why it matters

Class-level dict, no bound. A long-running workflow that sees many video ids leaks one namespace per extra video. Not a crash on the first video; unbounded growth after that.

Fix

#2834 — retain every namespace the instance touched; release all on close/__del__; refcount so two instances sharing a video id do not smash each other.