feat: enable vtu file support, improve testing suite, improve design condition rendering

[dragos-ana]

• Enables external vtu file support, see new default file. This is done in the same framework as for the Exodus files.
• Improves testing suite: we now test for different files with different geometry types: exo, vtu, legacy. Also, the vtu path
  is tested for, which more reliably verifies if the geometry of the yaml file was initialized
  correctly.
• Improves rendering of design conditions: threshold was replaced by the more reliable point filtering. Hence, only the relevant points / nodes are included, and not anymore ALL the cells containing these relevant points.

Interested parties: @tuchpaul, @LaSi5002

[Copilot]

Pull request overview

This PR adds support for VTU geometry files alongside existing Exodus file support, enhances the testing suite to cover multiple geometry file types (Exodus, VTU, and legacy formats), and improves design condition rendering by replacing threshold-based filtering with more reliable point-based filtering that only includes relevant nodes.

Key Changes:

• Implemented VTU file support with postprocessing logic similar to Exodus files
• Enhanced test coverage with parametrized tests across different file types and verification of VTU path initialization
• Improved design condition rendering accuracy by using direct point filtering instead of threshold-based cell selection

Reviewed changes

Copilot reviewed 12 out of 18 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/test_fourcwebserver.py	Refactored tests to use parametrization for testing multiple file types (DEFAULT, legacy, exo, vtu) and enhanced validation of server variables including VTU path verification
tests/files/tutorial_solid_vtu.4C.yaml	Added new test file for VTU geometry type with design conditions across different geometric entities
tests/files/tutorial_solid_exo.4C.yaml	Updated geometry file reference and added volume Dirichlet conditions for more comprehensive testing
tests/files/mat_transviso_viscoplast_refJC_log_substep.4C.yaml	Added new test file for legacy geometry format with viscoplastic material model
src/fourc_webviewer_default_files/tutorial_solid_vtu.4C.yaml	Added default VTU example file mirroring test file structure
src/fourc_webviewer_default_files/init.py	Updated default input file from Exodus to VTU example
src/fourc_webviewer/read_geometry_from_file.py	Added VTU file support infrastructure including postprocessing function, geometry type detection, unified mesh handling for exo/vtu files, and renamed methods for clarity
src/fourc_webviewer/input_file_utils/io_utils.py	Extended material specifier list to support mixture materials and growth strategies
src/fourc_webviewer/fourc_webserver.py	Improved design condition rendering using direct point filtering, removed unused code, adjusted sphere scaling factor, and cleaned up imports
requirements.txt	Updated package versions and changed fourcipp dependency to git URL
requirements.in	Changed fourcipp dependency from versioned to git URL

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[gilrrei]

Nice, just some minor refactoring comments, from Python perspective :)

[dragos-ana]

@c-p-schmidt and @gilrrei: Thank you for the thorough review!