Follow-up: remove per-batch offsets copy in variable full-zip decode #6027
Description
PR #6013 fixes a scan-full regression by slicing variable data per batch and rebasing offsets to 0.
As noted in review, downstream variable decompressors should theoretically be able to use offsets to determine the required decode range, which could let us avoid the per-batch offsets copy introduced in the fix.
The current fix is correct and improves performance, but we should investigate whether we can remove this extra offsets copy safely.