samples: rust: Add scoped debugfs sample driver

Adds a new sample driver `rust_scoped_debugfs` that demonstrates the
use of the scoped debugfs APIs.

The driver creates a `control` directory with two write-only files,
`create` and `remove`. Writing a name and a series of numbers to
`create` will create a new subdirectory under a `dynamic` directory.
This new subdirectory will contain files that expose the numbers as
atomic values.

Writing a name to `remove` will remove the corresponding subdirectory
from the `dynamic` directory.

This sample serves as an example of how to use the `debugfs::Scope`
and `debugfs::ScopedDir` APIs to create and manage debugfs entries
that are tied to the lifetime of a data structure.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250904-debugfs-rust-v11-7-7d12a165685a@google.com


[ Rename "scoped_debugfs" -> "debugfs_scoped", fix up
  Result<(), Error> -> Result. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>