Magma seqIndex wasted space may consume all compression gains

We noticed in CBSE-16847 that the sequence index wasted space was consuming half the total disk usage on a single node, 1TB of 2TB. This was a result of high compression(2X) in this case resulting in wasted space being allowed to grow up to the 50% fragmentation compared to the total data_size thus negating the gains made by compression.

The fix for this involves scaling WastedSpace usage during compaction trigger computation with compression ratio of L4 ie. logical size vs physical.

We will also have to add stats to help debugging this scaling if issues arise.