Add `tee_reader` / `tee_reader_with_options` in `rustfs-rio`: a
`TeePrimary` that drives the source and a `TeeSecondary` that observes
an identical copy of every chunk through a byte-bounded queue. The
primary returns `Pending` when the queue is full, so both sides advance
at the pace of the slowest consumer; it is meant for small objects only.
Termination: source EOF and errors propagate to the secondary with the
same `io::ErrorKind`; dropping the secondary turns the primary into a
pass-through; dropping the primary early fails the secondary with
`BrokenPipe` by default, or hands the remaining source to a background
drain task bounded by `max_drain_bytes` when
`TeeOptions::drain_on_primary_drop` is set. `TeeSecondary::into_stream`
exposes the queued `Bytes` chunks without an extra copy.
Includes a proptest equivalence test, backpressure, error, drop,
drain-limit and cancel-safety tests, and a criterion bench comparing
tee throughput against a direct read (64 MiB in 1 MiB chunks).
Zhengchao An
1dd81cf276