res_sorcery_memory_cache: Add support for maximum_objects.

This makes the "maximum_objects" option operational.

A heap has been added alongside the hash table in the cache. When
objects are added to the cache, they are also added to the heap.
Similarly, when objects are removed from the cache, they are removed
from the heap.

The heap's use comes into play when an item is to be added to a "full"
cache. When the cache is full, the oldest item is removed from the
cache, using the heap to determine the oldest item.

A unit test has been added that verifies that the maximum_objects option
works as expected and that the oldest object is removed from the cache
when an object beyond the maximum is added.

ASTERISK-25067 #close
Reported by Matt Jordan

Change-Id: I490658830e9c4cbf0b3051e4cdc4913cf9f1b73a