Magma compaction has race condition when doing explicit compactions

Magma has explicit compactions triggered by kvstore API call compactDB. It also has implicit compactions trigger by certain conditions within magma. Sometimes those implicit compactions can overlap with explicit compactions and pick up the compaction context. We need to make a copy of the compaction_ctx and when compactions see the compaction_ctx, they need to allocate their own copy of the eraserContext.