Update hypers in zundel notebook so it does not fail circleci tests

[agoscinski]

The zundel notebook takes too long in a cell, so the test always fails because of time exceed (@max-veit mentioned this is probably because of too much memory usage)

Changed max_radial to 6 and max_angular to 4 in the notebook to fix this. The parity plot and simulation still seems to reasonable. Now the zundel notebook runs in no time.

#!/bin/bash -eo pipefail
cd examples && PYTHONPATH=${PWD}/../build pytest --nbval-lax *.ipynb

============================= test session starts ==============================
platform linux -- Python 3.8.12, pytest-6.2.5, py-1.11.0, pluggy-1.0.0
rootdir: /root/project
plugins: nbval-0.9.6
collecting ... collected 215 items                                                            

Feature_selection_example.ipynb .................................        [ 15%]
MLIP_example.ipynb ........................                              [ 26%]
equivariant_demo.ipynb ................................................. [ 49%]
..............................                                           [ 63%]
nice_demo.ipynb ........................................                 [ 81%]
optimized_radial_basis_functions.ipynb .....................             [ 91%]
zundel_i-PI.ipynb .........

Too long with no output (exceeded 20m0s): context deadline exceeded

https://app.circleci.com/pipelines/github/cosmo-epfl/librascal/2812/workflows/261b797d-540b-404b-b850-60fb66353bba/jobs/24961

[agoscinski]

Have rerun it three times and it worked every time https://app.circleci.com/pipelines/github/cosmo-epfl/librascal/2813/workflows/a8c78c24-8ac6-416c-bcbc-8e7c6b5b7201/jobs/24982 https://app.circleci.com/pipelines/github/cosmo-epfl/librascal/2813/workflows/a8c78c24-8ac6-416c-bcbc-8e7c6b5b7201/jobs/24983 https://app.circleci.com/pipelines/github/cosmo-epfl/librascal/2813/workflows/a8c78c24-8ac6-416c-bcbc-8e7c6b5b7201/jobs/24984

[max-veit]

Ok, thanks - this should make automated testing of PRs much less of a pain.