Optional pytest and better-exceptions integration for MultipleFailures

[Zac-HD]

We now respect the pytest --tb={no,short,native,auto,long} configuration; or if you aren't using pytest but do have better-exceptions active we'll use that. Closes #3116.

As a bonus: tries to detect light-colored terminal backgrounds, and prints ghostwritten code with light-theme syntax highlighting. This doesn't always work, but it's a lot better than the status quo of assuming a dark background and there's a clear place for future improvements.

[rsokl]

If it isn't too much work, can you provide a minimal reproducible example so that I can be sure that I am exercising the pytest/better-exceptions functionality that this PR targets?

[Zac-HD]

# example.py
from hypothesis import given, strategies as st

@given(st.integers())
def test(x):
    assert x > 0
    assert x < 0

if __name__ == "__main__":
    test()

pytest example.py --tb=short
pytest example.py --tb=long

python example.py
BETTER_EXCEPTIONS=1 python example.py