The refactor exposes in-place `get_*_vector(workspace, buf)` overloads; exercise them
beside the allocating helpers and keep allocation probes on pre-filled buffers.
- Assert buffer aliases and equality against freshly extracted vectors.
- Replace generic `get_field` probes with direct NamedTuple field access.
New 294-line test file included in main test/runtests.jl:
- Tests refactored AssemblyMaterialWorkspace with compositional field design
- Tests field structure inference from material traits
- Tests workspace creation with correct field types
- Tests field access (backward compatibility)
- Tests multiphysics support preparation
- Validates zero allocations in workspace operations
Ensures assembly workspace refactoring maintains backward compatibility and performance.