rust: debugfs: support for binary large objects

rust: debugfs: support for binary large objects

Introduce support for read-only, write-only, and read-write binary files
in Rust debugfs. This adds:

- BinaryWriter and BinaryReader traits for writing to and reading from
  user slices in binary form.
- New Dir methods: read_binary_file(), write_binary_file(),
  `read_write_binary_file`.
- Corresponding FileOps implementations: BinaryReadFile,
  BinaryWriteFile, BinaryReadWriteFile.

This allows kernel modules to expose arbitrary binary data through
debugfs, with proper support for offsets and partial reads/writes.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Matthew Maurer <mmaurer@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>