Added CleanCache() method to the solver that deletes all the caches if
the total size grows above a certain (configurable) limit
(default: 500 MiB).
The function is called externally to handle errors (usually log or
ignore completely) and to avoid calling multiple times for multiple
depsolves of a single request.
The cleanup is extremely simple and is meant as a placeholder for more
sophisticated cache management. The goal is to simply avoid ballooning
cache sizes that might cause issues for users or our own services.
