chore(cu): remove unused drained process memory

[TillaTheHun0]

Background

During operation, the CU will drain LRU wasm memory into files, to free up space in its heap. If the corresponding ao process receives traffic, the CU will then "rehydrate" the cache entry for that process, by reading the memory in from the file.

When the CU shuts down, they files are effectively orphaned.

Problem

These WASM memory files can be quite large, and over time consume a nontrivial amount of disk. They are never cleaned up and are basically a one time use.

Solution

When the process wasm memory read from the file and subsequently is saved back into the LRU cache, the file that contained the drained memory should be deleted. Great care needs to be taken to ensure the files is not being used elsewhere. A lock can be used to ensure this is the case

Developer Notes

This deletion should be performed asynchronously, and fail gracefully.