Move In-Memory Arena Away from Skiplist

We performed some benchmarking of the storage stack in Sofia and discovered a few bottlenecks:

1. The materialized view builder sequentially seeks in the skiplist to build a view from the arena.  This is slow.
2. Skiplist seeking was eating a large portion of time.

If we migrate to an array of sample values, we can simply pass that off as a chunk to the view builder and let that tear through what it can.