Evaluate the effect of value separation on Magma's keyIndex point and range lookup

We disabled Magma's value separation as part of the CDC changes. This can result in a regression of Magma's key based point and range lookup performance if the value is under 32 bytes since we are now forced to lookup the seqIndex for all keys.

We need to evaluate the performance of value separation from a write amp, point/range lookup and backfill perspective to see if it is worth turning off value-separation under a certain value size. And to find an optimal value size for the separation.