[HyperElastic] Fix inverted Stable Neo-Hookean scene and add regression coverage

[lililii124]

Fixes #6220.

The inverted Stable Neo-Hookean example has conflicting topologies and develops non-finite states. This separates the initial inverted grid from the rest topology, computes mass on the tetrahedral rest mesh, and reduces the time step to 1e-5. Geometry, material parameters, total mass and fixed nodes are unchanged.

Adds a 100-step state regression and four material tests for negative-J stress and tangent consistency, including an analytical reflection case.

Validation used a Windows Release build in double precision. The 28 HyperElastic tests completed without failures. A 5,000-step simulation remained finite, with no fixed-node drift or inverted tetrahedra at the end. Repeating the state comparison reported zero error; the absolute-J and missing-force-field controls produced the expected test failures.

Scene validation used a native C++ harness with SOFA's simulation engine and official WriteState/CompareState visitors. The runSofa CLI, upstream Regression_test executable and cross-platform CI were not exercised.

Companion reference data: sofa-framework/Regression#142. The regression entry requires these files.

AI assistance was used for implementation, tests and validation. Requested label: pr: AI-aided.

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