Tests performance improvements

This is related to #280 (closed) but it is slightly different.

Some examples-as-tests are dramatically slow, especially in debug builds. It turns out that they do write a lot of files, which are not used during the test itself.

As an example (and I might be wrong) examples/tcp/tcp-validation.cc is writing all the logs all the time, even when launched as a test (--validate=1 --validation=<something>).

These traces are not actually parsed for the validation, so they're useless. However, they do slow down the script dramatically.

We should check the examples used as tests, and remove where possible any unnecessary write-to-file. The CI/CD workers are already slow enough, we don't need to slow them down more.