[IO] fail hard if the globalCompleter would drop a Future
Currently the globalCompleter would drop Futures which he is not able to submit to its SQ because io_uring_submit returned -EBUSY, signalizing a full CQ.
Additional small code changes:
- don't wrap assert in if constexpr(DEBUG)
- annotate Future completion in globalCompleter as unlikely
- use prepared Future count as unsigned
- remove redundant parenthesis
- introduce helper function for IoCOntext* tagging For now we fail hard if this hopefully unlikely case occurs.