block: unify block and fdmon io_uring Every AioContext has an io_uring context for file descriptor monitoring. In addition, block/io_uring.c also has an io_uring context for disk I/O. This patch series eliminates the extra io_uring context so that AioContext has a single io_uring context. Patch 2 introduces the aio_add_sqe() API for submitting custom io_uring SQEs. Patch 3 then replaces its io_uring context with the aio_add_sqe() API so that disk I/O requests share the AioContext's io_uring context. I will post performance results when they become available. Based-on: 20250326183340.1010531-1-stefanha@redhat.com