feat(rio): add bounded tee reader for one-read two-consumer paths (#7066)

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).

crates/rio/src/lib.rs

@@ -118,6 +118,12 @@ pub use hardlimit_reader::HardLimitReader;
 
 mod hash_reader;
 pub use hash_reader::*;
+
+mod tee_reader;
+pub use tee_reader::{
+    DEFAULT_TEE_MAX_DRAIN_BYTES, TeeDrainLimitExceeded, TeeOptions, TeePrimary, TeeSecondary, TeeStream, tee_reader,
+    tee_reader_with_options,
+};
 mod checksum;
 pub use checksum::*;