Previously, dns_answer_add() was O(n^2).
With this change dns_packet_extract() becomes ~15 times faster for some
extremal case.
Before:
```
$ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808
/home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok
real 0m15.453s
user 0m15.430s
sys 0m0.007s
```
After:
```
$ time ./fuzz-dns-packet ~/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808
/home/watanabe/downloads/clusterfuzz-testcase-minimized-fuzz-dns-packet-5631106733047808... ok
real 0m0.831s
user 0m0.824s
sys 0m0.006s
```
Hopefully fixes oss-fuzz#19227.
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19227
There isn't really much need to keep them separate. Anything which is a good
corpus entry can be used as a smoke test, and anything which which is a
regression test can just as well be inserted into the corpus.
The only functional difference from this patch (apart from different paths in
output) is that the regression tests are now zipped together with the rest of
the corpus.
$ meson configure build -Dslow-tests=true && ninja -C build test
...
307/325 fuzz-dns-packet:issue-7888:address OK 0.06 s
308/325 fuzz-dns-packet:oss-fuzz-5465:address OK 0.04 s
309/325 fuzz-journal-remote:crash-5a8f03d4c3a46fcded39527084f437e8e4b54b76:address OK 0.07 s
310/325 fuzz-journal-remote:crash-96dee870ea66d03e89ac321eee28ea63a9b9aa45:address OK 0.05 s
311/325 fuzz-journal-remote:oss-fuzz-8659:address OK 0.05 s
312/325 fuzz-journal-remote:oss-fuzz-8686:address OK 0.07 s
313/325 fuzz-unit-file:oss-fuzz-6884:address OK 0.06 s
314/325 fuzz-unit-file:oss-fuzz-6885:address OK 0.05 s
315/325 fuzz-unit-file:oss-fuzz-6886:address OK 0.05 s
316/325 fuzz-unit-file:oss-fuzz-6892:address OK 0.05 s
317/325 fuzz-unit-file:oss-fuzz-6897:address OK 0.05 s
318/325 fuzz-unit-file:oss-fuzz-6897-evverx:address OK 0.06 s
319/325 fuzz-unit-file:oss-fuzz-6908:address OK 0.07 s
320/325 fuzz-unit-file:oss-fuzz-6917:address OK 0.07 s
321/325 fuzz-unit-file:oss-fuzz-6977:address OK 0.13 s
322/325 fuzz-unit-file:oss-fuzz-6977-unminimized:address OK 0.12 s
323/325 fuzz-unit-file:oss-fuzz-7004:address OK 0.05 s
324/325 fuzz-unit-file:oss-fuzz-8064:address OK 0.05 s
325/325 fuzz-unit-file:oss-fuzz-8827:address OK 0.52 s
