By just storing the raw certificate we simplify the internal data
structure we use. In turn, this enables us to write better unit tests
using github.com/google/go-cmp where we can construct the expected
result and compare with that. (Yeah, in principle we could also
construct the full certificate but I'm not sure it's worth the effort
since we basically only care about the raw certificate.)
The general idea here is to make tracex more tested. Once it's more
tested, I will create separate structs for each event, which is
something that measurex also does. Once that is done, we can start
ensuring that the code in measurex and the code in tracex do the
same thing in terms of storing observations. When also this is done,
we can then rewrite measurex to use tracex directly.
The overall goal is https://github.com/ooni/probe/issues/2035.
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