daemon/worker: orphaned tasks prevention

unmarked as a Work In Progress

added 6 commits

• 1f9a11eb...aab8e6b0 - 5 commits from branch master
• 040ca990 - daemon/worker: orphaned tasks prevention

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This sometimes makes it crash on an assertion:

kresd: daemon/worker.c:1476: subreq_lead: Assertion `0' failed.

https://gitlab.labs.nic.cz/knot/knot-resolver/blob/master/daemon/worker.c#L1470

cc @anb

merged

mentioned in commit 23cd0fa1

We are not able to reproduce the crash and it passed all tests we invented so I'm going to merge this to expose it to more realistic workloads. Hopefully someone will be able to provide a reproducer.

added bug label