Add io tests that load WriteVTK with JuliaFEM and cover stub misuse, Hex8 and
Quad4 VTU output with nodal and cell data, suffix handling, and bad topologies.
- Add test/io/runtests.jl wrapper around the VTK-focused cases
- Implement test_writevtk.jl with structured mesh grids and negative cases
The in-tree `GmshReader` module is gone, so the dedicated IO test driver and
Tet4 fixture assertions are removed to keep the default suite aligned with
core dependencies.
- Delete `test/io/runtests.jl`, which only included `test_gmsh_reader.jl`
- Delete `test/io/test_gmsh_reader.jl`, which exercised `read_gmsh_mesh` and `get_surface_nodes` against bundled `.msh` data
New 23-line test file for postprocessing functionality:
- Tests field interpolation from elements
- Tests temperature field interpolation on 1D segment elements
- Tests interpolation at various points including boundaries
- Tests NaN handling for points outside domain
Simple test validating postprocessing interpolation works correctly.
Jukka Aho