bindings: rust: mark all owning types as `Send`

bindings: rust: mark all owning types as `Send`

The thread-safety rules of libgpiod allow individual object instances to
be used from different threads. So far, this was not actually possible
with the Rust bindings. Not being `Send` disallowed the user to transfer
the ownership to different threads.

Rust also has a `Sync` marker. That one would even allow sending
references of objects to other threads. Since we wrap a lot of C
functions with `fn foo(&self)` signatures, that would not be safe.
libgpiod does not allow concurrent API calls to the same object instance
- which Rust would allow for read-only references. Thus, we do not
define that one.

Chip was already modeled correctly.

line::Info is not marked as Send since it may either be owning or non-
owning. That problem is fixed as part of a separate pull request [1].

[1] https://lore.kernel.org/r/20230927-rust-line-info-soundness-v1-0-990dce6f18ab@linaro.org

Link: https://lore.kernel.org/r/CVHO091CC80Y.3KUOSLSOBVL0T@ablu-work
Signed-off-by: Erik Schilling <erik.schilling@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>