Tutorial updates for v163

[lilianschuster]

• updated to 2025.6 gdirs. For some notebooks, used other borders to minimise the necessary amount of notebooks.
• removed quite a few typos, wrong links ...
• also removed the Outdated maintenance banner #141 issue
• These notebooks still need to be checked, once the new gdirs are all available: "preprocessing_errors.ipynb", "inversion.ipynb" (check where "todo" is mentioned)
• In the notebook "observed_thickness_with_dynamic_spinup.ipynb", we have to use now the "non-spinup" preprocessed gdir. That means we have to create the spinup for that glacier in the notebook. I did that (but I may have missed something). The results look a bit different to the 2023.3 plots. @pat-schmitt, maybe you can check the code lines where I added "todo"?

[fmaussion]

Thanks @lilianschuster ! Will publish these and ask the community for feedback