Updates to meet myst --strict building requirements

[jukent]

Need to suppress Matplotlib string output
Excludes some links from link checker
Replaces broken gif paths

@cyschneck I couldn't find a replacement for https://upload.wikimedia.org/wikipedia/commons/6/6f/Programming123najra.gif so I simply removed it. Please lmk if you have a new gif path. Unfortunately once I double clicked the markdown cell the gif no longer would render for me, so I don't know what the gif was supposed to be of. If you can download this gif and add it into the repository _static/ folder that would be great.

[github-actions]

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[jukent]

I'm not sure why https://www.mathworks.com/help/wavelet/gs/what-is-a-wavelet.html is failing link checks, when it resolves just fine AND when it is in the list of URLs to ignore in link checking. Might need another pair of eyes.

E: It was hard to see, but there was an extra () around the link. Hopefully that does it. Might not need to be in the ignored links now, since the error was something else.

[cyschneck]

[cyschneck]

The existing gif was silly, but to keep the style similar on each page with a header gif. Not sure if this is showing up, but I posted:

<p align="center">
  <img src="../../static/Programming123najra.gif" alt="Animation of hacking" />
</p>

[cyschneck]

I added in the gif to the main wavelet-cookbook, so it should be available through a branch update