Redis [NEW] Module API for async-free of memory

The problem/use-case that the feature addresses

Currently, the module API only allows to async-free an entire key (RM_Unlink) There should be a way to async-free any pointer (not a single allocation, but rather some sort of complex data structure with many individual allocations)

Description of the feature

Add a new API RM_AsyncFree which takes a pointer, a free_effort CB, and a free CB