Implement vector graphics and adjust figure sizes

[albertomercurio]

Checklist

Thank you for contributing to Tutorials for Quantum Toolbox in Julia! Please make sure you have finished the following tasks before opening the PR.

• Please read Contributing to Quantum Toolbox in Julia.
• The (last update) date were modified for new or updated tutorials.
• For new tutorials, a Version Information section was added at the end and displays the output of versioninfo().
• All tutorials were able to render locally by running: make render.

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Description

The current version of the website shows very low quality plots, everyone with a different width. Here I set the vector graphics, in order to show high-quality plots, and I also set a default witdth, common to all plots.

I also changed the date of every file to last-modified, as I think it is a smarter way to keep track of dates.

[github-actions]

PR Preview Action v1.6.1
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[ytdHuang]

I remember that setting Date as last-modified is incorrect. Since it records the render date.

[albertomercurio]

It seems that it is only a problem of the GitHub Action

quarto-dev/quarto-cli#5899

They suggest to add the following script to the action, in order to restore information of the last modification time from git commits

https://stackoverflow.com/a/55609950

I'm trying to implement it

[albertomercurio]

Also, I don't think we need the cardinalby/export-env-action action, as Quarto looks automatically at the _environment file when rendering.