Write better tests for Pipeline.run()

[silvanocerza]

Pipeline.run() tests are not as reliable as we want, there are some corner cases that are not covered and in the past weeks we found and fixed quite some bugs. See #7531, #7434 and #7426.

We need to rewrite some tests to be simpler and easier to understand, and also leverage tracing to verify Components are run in the expected order.

Some tests can also be removed too.