Make CLASS, TYPE converting functions thread-safe

src/knot/zone/zone-dump-text.c

src/knot/zone/zone-load.c

src/libknot/nameserver/name-server.c

src/libknot/packet/packet.c

src/libknot/packet/response.c

src/libknot/rrset.c

src/libknot/updates/xfr-in.c

src/libknot/util/debug.c

src/libknot/util/descriptor.c

src/libknot/util/descriptor.h

src/libknot/zone/zone-contents.c

src/libknot/zone/zone-diff.c

src/tests/libknot/realdata/libknot/response_tests_realdata.c

src/tests/libknot/realdata/libknot/rrset_tests_realdata.c

src/tests/libknot/realdata/libknot_tests_loader_realdata.c

src/zcompile/parser-util.c

src/zcompile/zcompile.c