Add events.lhe comparison in tlau tests

[valassi]

I am completing multi build gridpacks and tlau tests that go with them #945

Now I produce events.lhe with different backends in parallel

One step that is missing is comparing that I get the same events.lhe from different backends. The cpp SIMDs may already be compared to one another, but they cannot be compared to fortran because of issue #872.

This task can only be done after merging #935 or an alternative fix

I create this task as a reminder for myself