Exclude setup/teardown from leak checking

[pv]

Currently, the leak checking encompasses the whole setup/call/teardown cycle. This is maybe not optimal, since some pytest fixtures appear to leak, and those leaks are usually not of interest.

It would be possible to split the refleak run cycle todo

setup()
cleanup()
before = get_counts()
test()
cleanup()
after = get_counts()
deltas = after - before
teardown()

instead of the current

setup()
test()
teardown()
cleanup()
after = get_counts()
deltas = after - before
before = after

but it comes at the price of two cleanups, which I guess are required before "get_counts" for stable numbers.

[pv]

Not sure how feasible this is though: Calling via the hook pytest_runpytest_call enables e.g. the logging fixture (on by default) which hold references from call to teardown and would seem to leak if done like this. OTOH, calling directly without the hook disables output capture, so also not ok.