WCAB 0.9.0 — iterative calculation coverage

WCAB 0.9.0 adds a deterministic iterative-calculation case. Its direct self-referencing formula and downstream local reference are unchanged while calcPr/@iterate moves from false to true; explicit bounds remain 100 iterations and a 0.001 delta. WCAB validates stored OOXML and formula text only: it does not calculate the circular model, claim convergence, report a terminal value, or assert numerical correctness.\n\nValidation: 24 cases, 26 facts, 43 tests on Python 3.12/3.13 locally; hosted CI passed on Python 3.10/3.13. The optional FormulaFence reference pass matched all 25 mappable facts and all three coverage declarations; one structural-equivalence annotation remains intentionally unmapped.