blkio: bump version to 0.3.0

API changes:
- Add support for adding/removing queues to/from a started blkio via
  blkio_add_queue()/blkio_remove_queue() and
  blkio_add_poll_queue()/blkio_remove_poll_queue().

Crate dependency changes:
- io-uring 0.5.10 is now the minimum version. I treated this as a major
  change and therefore bumped blkio's version to 0.3.0.