rust: io: move `Io` methods to extension trait

`Io` trait now has a single required method with many more provided
methods. Provided methods may want to rely on their implementations to not
be arbitrarily overridden by implementers for correctness or soundness.
A good example is the `size` method, it may be relied by unsafe code and
thus must be consistent with the metadata obtained from `as_ptr`.

Thus, create a new trait to host `size` method, extract existing provided
methods to the new trait, and provide a blanket implementation. This
pattern is used extensively in userspace Rust libraries e.g. `tokio` where
`AsyncRead` has minimum methods and `AsyncReadExt` is what users mostly
interact with.

To avoid changing all user imports, the base trait is renamed to `IoBase`
and the newly added trait takes the existing `Io` name.

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Suggested-by: Danilo Krummrich <dakr@kernel.org>
Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Daniel Almeida <daniel.almeida@collabora.com>
Link: https://patch.msgid.link/20260706-io_projection-v6-12-72cd5d055d54@garyguo.net
[ Add comment explaining the purpose of the Io blanket implementation.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

0 files changed, 0 insertions, 0 deletions