[MeshioPlusPlusApplication] Multi-format mesh I/O, mesh operations and field-data operations

[loumalouomega]

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name: ✨ Feature
about: MeshioPlusPlusApplication: multi-format mesh I/O, mesh operations and field-data operations

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📝 Description

Adds MeshioPlusPlusApplication, wrapping the meshio++ library to bring multi-format mesh I/O, native read/write support for ~35 mesh file formats (vtu, vtk, gmsh, med, xdmf, abaqus, medit, stl, obj, su2, tecplot, unv, ...) in addition to .mdpa., and a full mesh/data operations layer into Kratos, consumed as a normal external dependency (nothing vendored — built and installed separately, linked via find_package(meshioplusplus CONFIG REQUIRED COMPONENTS CXX)).

I/O (MeshioPlusPlusIO)

• 41 readable / 43 writable formats, including the Kratos-native mdpa, resolved explicitly or by extension.
• Sub model parts map to meshio++ named regions (nesting included); registered entity names (SmallDisplacementElement3D4N, ...) and Properties material data are preserved across a round trip instead of degrading to the generic cell-type name / losing values.
• Transient output: single-file XDMF temporal collections, file series for every other format, append-safe restart and crash-safe flushing.
• kratos/python_scripts/python_solver.py's _ImportModelPart now delegates any input_type the core doesn't handle itself to this application (lazily imported, so the core has no hard dependency on it).

Mesh operations (MeshioPlusPlusMeshOperations)

• Data-driven through Parameters, one "operation" name per meshio++ verb: clean, transform, convert_cells, refine, decimate, smooth, reorder, extract_surface, extract_skin, crop_bbox, crop_halfspace, slice, isosurface, attach_quality, split, partition, stats, quality, plus Merge, Diff, ComputeStatistics/Quality/Bandwidth as separate entry points.
• Field-data operations layer: data_calc, data_condition, data_manage, data_info, point_data_to_cell_data, cell_data_to_point_data, and cross-mesh Interpolate (nearest/barycentric sampling of one mesh's field data onto another's geometry).
• Nodal/elemental/conditional variables, flags and ids now flow through the operations layer end-to-end (opt-in via the same settings MeshioPlusPlusIO uses), which also makes isosurface usable in practice for the first time. A result array survives the trip back into Kratos only when its name matches a registered Variable — documented as a hard framework constraint, not a gap (e.g. attach_quality's own "quality:scaled_jacobian" naming never round-trips).

Python surface

• Modelers: MeshioInputModeler, MeshioOperationModeler (generic, covers every single-source operation), MeshioInterpolateModeler (dedicated, since Interpolate needs two independent source model parts and doesn't fit the generic shape).
• MeshioOutputProcess for transient/steady output from a solver's Parameters.
• Registered in python_registry_lists.py and .github/workflows/ci_apps_linux.json.

Docs & tests

• applications/MeshioPlusPlusApplication/README.md plus 5 pages under docs/pages/Applications/MeshioPlusPlus_Application/ (Overview, the three modelers, Mesh Operations, Output Process).
• 79 C++ GTest cases (tests/cpp_tests/) and 56 Python unittest cases (tests/), covering format round trips, transient output, every mesh/data operation, field-data staging and write-back, the write-back constraint, and all three modelers.
• meshio++ version handling is pinned on MESHIOPLUSPLUS_ABI_VERSION (currently 3, meshio++ v9.2.0+) rather than an exact release, so a release that can't affect a compiled consumer needs no rebuild; a real mismatch fails at configure/link time rather than silently.