Follows hyperfile 0.10.3: a malformed staging URI, and a HeadObject without a
usable Date or Last-Modified, are errors there instead of a panic or a hang.

S3Cleaner::with_client no longer turns "s3://" into "s3:/" when trimming a
trailing slash, so it is refused as an incomplete URI, the right reason.

Requires hyperfile 0.10.3.