documentation: add helpers for marimo things to be shared across notebooks

[superlopuh]

We want to have more than one notebook, and a consistent way of showing things in them. I think a helpers file would be a good way to do that.

The main question is where we want the code to live, I think xdsl.utils.marimo makes sense, but I'm open to suggestions.

[math-fehr]

xdsl.docs.marimo?
Is there a reason we want to put them all in the same place btw? Compared to order them by doc, tutorial, etc..?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.31%. Comparing base (b943df3) to head (5005e6f).
Report is 1 commits behind head on main.

Additional details and impacted files

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- Coverage   91.32%   91.31%   -0.01%     
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  Files         467      468       +1     
  Lines       58543    58546       +3     
  Branches     5652     5652              
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  Hits        53463    53463              
- Misses       3628     3631       +3     
  Partials     1452     1452              

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[superlopuh]

Hmm, it's really just reusable UI elements, not the full notebooks. The notebooks will still live in the docs folder, and you're right that they should be grouped together in some way. This seems like an orthogonal proposal, unless I'm misunderstanding you.

[math-fehr]

Nope my bad, I misunderstood you, looks good how it is now!