* fix(s3): skip directories before marker in ListObjectVersions pagination
ListObjectVersions was re-traversing the entire directory tree from the
beginning on every paginated request, only skipping entries at the leaf
level. For buckets with millions of objects in deep hierarchies, this
caused exponentially slower responses as pagination progressed.
Two optimizations:
1. Use keyMarker to compute a startFrom position at each directory level,
skipping directly to the relevant entry instead of scanning from the
beginning (mirroring how ListObjects uses marker descent).
2. Skip recursing into subdirectories whose keys are entirely before the
keyMarker.
Changes per-page cost from O(entries_before_marker) to O(tree_depth).
* test(s3): add integration test for deep-hierarchy version listing pagination
Adds TestVersioningPaginationDeepDirectoryHierarchy which creates objects
across 20 subdirectories at depth 6 (mimicking Veeam 365 backup layout)
and paginates through them with small maxKeys. Verifies correctness
(no duplicates, sorted order, all objects found) and checks that later
pages don't take dramatically longer than earlier ones — the symptom
of the pre-fix re-traversal bug. Also tests delimiter+pagination
interaction across subdirectories.
* test(s3): strengthen deep-hierarchy pagination assertions
- Replace timing warning (t.Logf) with a failing assertion (t.Errorf)
so pagination regressions actually fail the test.
- Replace generic count/uniqueness/sort checks on CommonPrefixes with
exact equality against the expected prefix slice, catching wrong-but-
sorted results.
* test(s3): use allKeys for exact assertion in deep-hierarchy pagination test
Wire the allKeys slice (previously unused dead code) into the version
listing assertion, replacing generic count/uniqueness/sort checks with
an exact equality comparison against the keys that were created.
