feature request: support submit multi sqe with link at once

currently the [submit](https://docs.rs/compio/latest/compio/runtime/fn.submit.html) only support submit 1 op

however, in io-uring, the kernel support submit a batch sqe with [IO_LINK](https://docs.rs/io-uring/latest/io_uring/squeue/struct.Flags.html#associatedconstant.IO_LINK)

this allow user submit a batch sequence ops, and wait them complete, with only 1 submit call

A common case is when you have a batch of data to write into the fd which is datagram mode