Add raw_async_io_tests.rs with punch_hole, write_zeroes, and
multiple_operations helpers that take &mut dyn AsyncIo + &mut File.
These are raw-backend-specific. They verify data by reading the
underlying file directly, which only works for plain file backends
without container format metadata.
Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
