Consider shrinking SLC cache size now that max list is much larger

[dlongley]

Max list size (totally randomized) is going to be 32MiB * 1.33 (base64url-encoding 33% bloat). This means a cache with 1000 of these would use 32 GiB of RAM which we should presume, I think, is too large for most deployments. This means we need to cut this by a factor of 10 or have more complex cache options (and maybe some code) that rely on the size of each list and we just set a maximum cache size instead.