Faster tests and leaner scripts

[abhijeetgangan]

Currently there are too many examples and since they are all ran in CI especially with the machine learning force-fields they are extremely slow. Solutions could be:

• Combine scripts into one tutorial highlighting the functionality along with commentary.
• Swap for faster force-field or even use Lennard-Jones(?).

[thomasloux]

I would use Lennard-Jones only. And keep only one with a MLIP to perform NVT