Memory Leaks and consumption

I think we must address memory leaks not only by buying more RAM ;-). Otherwise we might need 128 Gb for all wafer tests with ITkPixV1. One example: the numpy arrays from the chip masks are never garbage collected. The run of software tests requires > 10 Gb.

This is unfortunately not trivial to debug and not trivial to understand.

It might be that the python gc cannot re-solve our creative "every class knows every class" relationship scheme. Although, this would surprise me. In addition with multiprocessing things get very complicated.

It was related to multi-threading. Leaks for bdaq usage are likely fixed with !419 (merged). However, unit tests still heavily leak and #450 (closed) still is an issue. Likely related to coverage/pytest packages itself.