rust: configfs: require thread-safe callback data

The Rust configfs abstractions do not fully constrain callback data for
cross-thread use. Add the missing `Send` and `Sync` requirements.

Specifically, make the following changes:

1. Require `Data: Send` when implementing `Send` for `Subsystem<Data>`,
   since the subsystem stores its data by value.
2. Make `GroupOperations` a `Sync` supertrait because `make_group` and
   `drop_item` receive `&self` from foreign threads. Require `Child: Send`
   because configfs may release child groups on an arbitrary thread.
3. Require `AttributeOperations::Data: Sync` because its callbacks receive
   `&Data` from foreign threads.
4. Update the safety comments in FFI callbacks that call `get_group_data`
   to cite these bounds as justification for sharing the returned
   references with the callback thread.
5. Remove redundant `Child: 'static` bounds from `GroupOperationsVTable`
   and `new_with_child_ctor`.

Fixes: 446cafc295bf ("rust: configfs: introduce rust support for configfs")
Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/Should.20add.20Data.3A.20Send.2FSync.20bounds.20in.20configfs.3A.3ASubsystem.3F/with/623719979
Assisted-by: Gpt-5.6 Sol
Signed-off-by: Yilin Chen <1479826151@qq.com>
Link: https://msgid.link/tencent_5449081195EDDF5726C709CF648DD4044A08@qq.com
[ Andreas: Add Send/Sync bounds for `Group<Data>`, add `Send` bounds to
`GroupOperationsVTable`, `ItemOperationsVTable` and `ItemType` macro
implementation. ]
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>

0 files changed, 0 insertions, 0 deletions