* s3: sort ListMultipartUploads by key and honor key-marker
* s3: skip upload folders without an object key in ListMultipartUploads
* s3: order same-key multipart uploads by initiation time
The upload id suffix is now a time-ordered UUIDv7, so sorting by upload id lists a key's uploads oldest first, like S3. Pagination is unchanged: ordering and the upload-id-marker comparison share the same key.
selectMultipartUploads now builds the whole result, including NextKeyMarker and NextUploadIdMarker, and the pagination test pages with the response markers.
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Co-authored-by: Chris Lu <chris.lu@gmail.com>