documentation: (marimo) move pipeline_html helper to utils

[superlopuh]

Creates a unified way of presenting the intermediate stages of compilation in the marimo notebooks, together with optional descriptions of what's happening. I'm not super happy with the way it's presented right now, but we can iterate on it once it's in, and all the notebooks will benefit from it at the same time. I'm relatively sure that this API is all we need, but we can change it later also.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.27%. Comparing base (460bd6e) to head (eba339c).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3719      +/-   ##
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- Coverage   91.31%   91.27%   -0.04%     
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  Files         468      468              
  Lines       58549    58595      +46     
  Branches     5652     5655       +3     
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+ Hits        53463    53485      +22     
- Misses       3634     3658      +24     
  Partials     1452     1452              

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