lib/resolve: even better support for forwarder choice

- sort the list instead of just picking the best one
- prefer unknown RTTs to probe them
- verbose output of the choice

Fixes https://gitlab.labs.nic.cz/knot/resolver/issues/125
Fixes https://gitlab.labs.nic.cz/knot/resolver/issues/208
6 jobs for <span class="ref-name">fw-multi-target</span> in 77 minutes and 37 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
canceled #72986
docker linux amd64
build:linux:amd64

passed #20032
docker linux amd64
build:linux:amd64

00:00:35

 
  Test
passed #20034
docker linux amd64
deckard:linux:amd64

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passed #20036
docker linux amd64 allowed to fail
respdiff:linux:amd64

01:17:06

passed #20033
docker linux amd64
test:linux:amd64

00:00:23

canceled #20035
docker linux amd64 allowed to fail
respdiff:linux:amd64

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