[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.
17 jobs for submit_fail_hard in 9 minutes and 45 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Smoke Test
passed smoke-test #307669

00:06:51

passed static-analysis-with-emper-io #307670

00:06:39

 
  Test
canceled test-clang #307674

00:02:52

canceled test-clang-debug #307676

00:02:52

canceled test-clang-release #307675

00:02:52

canceled test-clang-sanitizer-undefined #307680

canceled test-do-not-log-timestamp #307684

canceled test-gcc #307671

00:02:53

canceled test-gcc-debug #307673

00:02:53

canceled test-gcc-release #307672

00:02:53

canceled test-laws #307681

canceled test-laws-release #307682

canceled test-locked-ws-queues #307685

canceled test-with-stats #307678

00:02:51

canceled test-with-userspace-rcu #307679

canceled test-worker-no-sleep #307677

00:02:52

canceled test-worker-wakeup-strategy-all #307683