Add the FFPB_KPFM example

[mondracek]

• example/FFPB_KPFM/ directory created
• contains params.ini (parameters for the KPFM scan), input_plot.xyz (atom positions in the FFPB molecule), and run.sh (scrip to run the KPFM simulation)
• Download of LOCPOT_V?.xsf (the Hatree potentials) from Zenodo included in example/FFPB_KPFM/run.sh, using wget
• The dataset version in ppafm/ppafm/data.py updated.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a171cf6) 46.45% compared to head (7d73ca4) 46.44%.

:exclamation: Current head 7d73ca4 differs from pull request most recent head a404fd4. Consider uploading reports for the commit a404fd4 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #255 +/- ## ========================================== - Coverage 46.45% 46.44% -0.01% ========================================== Files 35 35 Lines 5179 5180 +1 ========================================== Hits 2406 2406 - Misses 2773 2774 +1 ``` | [Flag](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | Coverage Δ | | |---|---|---| | [python-3.10](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | `46.45% <ø> (ø)` | | | [python-3.11](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | `46.42% <ø> (ø)` | | | [python-3.12](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | `46.42% <ø> (?)` | | | [python-3.7](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | `46.25% <ø> (?)` | | | [python-3.9](https://app.codecov.io/gh/Probe-Particle/ppafm/pull/255/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle) | `46.34% <ø> (?)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Probe-Particle#carryforward-flags-in-the-pull-request-comment) to find out more.

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[mondracek]

@ondrejkrejci , I think I need your review so that I could merge.