rust: block: require `Sync` for `Operations::QueueData`

The queue data installed in a `GenDisk` is stored in the request queue and
handed back to the driver as a shared borrow through the `queue_rq` and
`commit_rqs` callbacks. Both callbacks obtain that borrow via
`ForeignOwnable::borrow` and may execute concurrently on several CPUs,
since the block layer runs one hardware queue per CPU. That means a shared
reference to the same queue data can be live on multiple threads at once,
which is only sound when the referent is `Sync`.

The initial `GenDisk` private data support omitted this bound, so a
driver could install a non-`Sync` type as queue data and then access
it concurrently from multiple CPUs without synchronization. Add a
`Sync` bound to the `QueueData` associated type to rule that out.

Fixes: 90d952fac8ac ("rust: block: add `GenDisk` private data support")
Cc: stable@vger.kernel.org
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://msgid.link/20260608-queue-data-sync-v1-1-0efff051aaf3@kernel.org
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>