Add Matrix4f affine inverse round-trip test

[boni-teppanyaki]

Summary

Adds an initial Matrix4fTest for com.jme3.math.Matrix4f, which previously had no dedicated test suite.

The test builds a typical affine transform using translation, scale, and rotation via setTransform, inverts it with invert(), multiplies the transform by its inverse with mult(), and verifies the result is approximately Matrix4f.IDENTITY.

Motivation

Matrix4f is used throughout jMonkeyEngine for world/view/projection matrices, camera math, skinning, shadows, and collision transforms. However, it currently has limited direct test coverage. This test introduces a basic mathematical property of affine transforms to exercise several important methods together, and provides a starting point for future, more comprehensive Matrix4f tests.

[gemini-code-assist]

Code Review

This pull request introduces a new unit test for Matrix4f that verifies the inversion of an affine transform containing translation, scale, and rotation. The reviewer suggested enhancing the test's robustness by checking the identity property for both left and right multiplication and adding descriptive failure messages to the assertions for better diagnostics.

[gemini-code-assist]

To make the test more robust and provide better diagnostics on failure, consider checking the inverse multiplication on both sides (transform * inverse and inverse * transform) and adding a failure message to the assertion that includes the actual result. This is standard practice for inversion tests to ensure the mathematical property holds in both directions.

        final Matrix4f product = transform.mult(inverse);
        assertTrue(product.isSimilar(Matrix4f.IDENTITY, 1e-4f),
                () -> "transform * inverse should be identity, but was:\n" + product);

        final Matrix4f inverseProduct = inverse.mult(transform);
        assertTrue(inverseProduct.isSimilar(Matrix4f.IDENTITY, 1e-4f),
                () -> "inverse * transform should be identity, but was:\n" + inverseProduct);

References

1. Issues found in test code should be reported with a reduced priority, at most medium.