[T1] ABF/ABFPlusPlus tests need a multi-interior-vertex mesh fixture

[csparker247]

Summary

All parameterization tests use a 4-vertex pyramid with exactly one interior vertex. This masks any bug that requires 2+ interior vertices (including #6 / B1). Tests must include a larger mesh with multiple interior vertices.

Required Additions

1. A ConstructGrid<MeshType>(rows, cols) fixture in tests/src/Utils.hpp (e.g. a 4×4 grid with 4 interior vertices)
2. ABF_MultiInterior and ABFPlusPlus_MultiInterior tests on this mesh
3. A test with 0 interior vertices (single triangle) — should not crash
4. A test verifying behavior when maxIters is reached without convergence

Note

This track should be completed before fixing #6 (B1) per TDD policy — the failing test should come first.

Conductor Track

T1