New 319-line test file for LinearElastic material model:
- Tests material construction and parameter validation
- Tests Lamé parameters (λ, μ) computation
- Tests stress computation: uniaxial, pure shear, hydrostatic
- Tests tangent modulus (4th-order elasticity tensor)
- Validates symmetry, isotropy, and physical properties
- Tests simplified interface (without state, Δt)
- Validates zero-allocation and type stability
Comprehensive test for Hooke's law implementation essential
for linear static and dynamic analysis.