The offsets were meant to speed-up the repeated dns_name operations, but
it was experimentally proven that there's actually no real-world
benefit. Remove the offsets and labels fields from the dns_name and the
static offsets fields to save 128 bytes from the fixedname in favor of
calculating labels and offsets only when needed.
Since this is very sensitive code which has often had security
problems in many DNS implementations, it needs a decent amount of
validation. This fuzzer ensures that the new code has the same output
as the old code, and that it doesn't take longer than a second.
The benchmark uses the fuzzer's copy of the old dns_name_fromwire()
code to compare a number of scenarios: many compression pointers, many
labels, long labels, random data, with/without downcasing.