Add a tutorial about vtu mesh input in our documentation

[amgebauer]

This PR adds a tutorial on VTU mesh input in our documentation. I hope I explain everything that is relevant.

Next week in the community meeting, I will present the tutorial in a short TGM (and a related python project) and answer questions.

I also extended a bit the plotting functionality in our documentation. We can also do now more complex plots (see the new tutorial). In this case, I'm plotting two meshes (the mesh itself with glyphs indicating the fiber direction). We are now able to plot anything that the plotter in pyvista can plot. We just forward all calls to pyvista and return a reference to the plotter-class:

{% set mesh = read_mesh("solid/tutorial_vtu.vtu") %}
{{ plotter(aspect_ratio=2/1)
    .add_mesh(mesh, show_edges=True)
    .add_mesh(mesh.glyph(orient="collagen_fiber", factor=0.5), color="red")
    .make() }}

[Copilot]

Pull Request Overview

This PR adds a comprehensive tutorial demonstrating how to use VTU (VTK Unstructured Grid) file format for mesh input in 4C, using a solid mechanics example featuring a living soft tissue with collagen fibers.

Key Changes:

• Enhanced plotting functionality with a new PlotBuilder class that enables flexible, chainable plot construction for documentation
• Added VTU mesh input tutorial with detailed explanations of block definitions, boundary conditions via point-sets, and field definitions
• Extended testing framework to support dependency checks (e.g., VTK requirement) for tutorial tests

Reviewed Changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
utilities/four_c_python/src/four_c_documentation/render.py	Adds PlotBuilder class for flexible plot construction, refactors plotting functions, and adds read_mesh helper for loading VTU files in templates
tests/tutorials/solid/tutorial_solid_vtu.4C.yaml	New tutorial input file demonstrating VTU mesh usage with complex material models and boundary conditions
tests/list_of_tests.cmake	Registers the VTU tutorial test with VTK dependency requirement
doc/documentation/src/tutorial_templates/tutorials.rst	Updates tutorial listing to include the new VTU tutorial
doc/documentation/src/tutorial_templates/tutorial_vtu.md.j2	Tutorial content explaining VTU file format usage, including blocks, point-sets, and field definitions
cmake/functions/four_c_testing_functions.cmake	Extends four_c_test_tutorial function to support REQUIRED_DEPENDENCIES parameter

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[c-p-schmidt]

Thank you for providing this tutorial!