Fix the Python test suite and the zero-density pipeline

[Chessing234]

Two things are broken on main, both easy to hit.

python tests/test_all.py never reaches an assertion. tests/test_affine2.py imports large_values.max_of, removed in "Remove redundant code" (Oct 2024) along with the affine max machinery, and test_all.py imports that module first. I rebuilt the same edge case against what survived — Affine2/Piecewise.min_with — with a value check against the naive minimum, so it still tests something.

lv_zlv_to_zd crashes part-way through. #194 made try_union raise on an input with extreme rays. But Region._as_disjoint_union_poly uses try_union as a merge attempt and relies on the documented None return to keep the pieces separate, so the raise aborts the caller instead of degrading. Returning None there restores the pipeline and still never produces a wrong envelope. That same raise also aborted run_union_test, which calls try_union on an unbounded pair and drops the result.

Evidence, on python 3.13 with pycddlib<3:

• before: python tests/test_all.py stops at the test_affine2 import; after: reaches "All test cases passed."
• before, on a clean checkout of main:

hs = Hypothesis_Set()
hs.add_hypothesis(lv.large_value_estimate_L2)
hs.add_hypotheses(literature.list_hypotheses(hypothesis_type="Zeta large value estimate"))
zd.lv_zlv_to_zd(hs, Interval(frac(1,2), 1), tau0=frac(3))

raises ValueError: Polytope.try_union only supports finite polytopes; with this branch it returns A(x) \leq 7/6 - x/3 on [1/2,1).