Reduce memory usage of the cache

The LIRS cache calculates the estimated number of cells using the cache size and the average entry size, and allocates empty arrays accordingly.

Currently, the LIRS cache uses a default entry size of 100 bytes, which is relatively low. Because of that, even an empty cache needs quite a lot of memory.

I found the average size of the entries is around 2000 for our unit tests. Using this average size should reduce memory usage a lot.