Persisted disk cache for cardinality queries

[keski]

The FederationAccessManagerWithCache currently maintains cardinality query results in an in-memory cache. This issue concerns implementing a basic disk-based caching mechanism that persists cardinality queries and their results to disk. This will enable CLI-based executions to share a simple persistent cache across runs.

Future enhancements will introduce features such as time-based eviction policies to improve cache management.

[keski]

There is now a basic implementation (FederationAccessManagerWithPersistedDiskCache) including tests in this branch. Note that I've only implemented the caching of SPARQL cardinality requests at this time. I based the implementation on a modified version of the FederationAccessManagerWithCache.

@hartig, it would be great if you could provide feedback on the general structure of the code, but especially on the tests since I felt they were a bit tricky.

[hartig]

Please create a PR. That makes it easier for me to provide feedback.