adds mesh io

[HenningScheufler]

Motivation

WHAT is it, WHY it is needed. 😘

[github-actions]

Thank you for your PR, here are some useful tips:

• If this is your first PR, please add yourself to the AUTHORS.md file
• Use labels to change the workflow behavior. Set auto-fix to automatically apply fixes, full-ci for a comprehensive set of tests and sanitizer runs, ready-for-review to show that you're done and need a review.
• I deployed a test documentation to https://exasim-project.com/NeoN/Build_PR_462
• For full-ci builds benchmark results are available at https://github.com/exasim-project/NeoFOAM-BenchmarkData/462
• Also check if the GPU pipelines on https://gitlab-ce.lrz.de/greole/neon/-/jobs are successful.