Consider auto-pruning to configured cache maximum size

[nathan-joslin]

Currently ace-dt does not prune its cache, requiring users to manually run ace-dt util prune or rm -r <cache-path>. As a result, without direct user actions the cache grows indefinetly.

We should consider using the existing cache prune max field in the configuration to "auto-prune" after ace-dt runs.

Note that some users utilize a shared cache, which may cause data races if the cache is pruned while simultaneously being used. Such an occurrence would be extremely rare, although possible.