Docs: add example coffee table with nanoplots

[machow]

This PR adds the coffee table example from https://github.com/machow/coffee-sales-data/

Note these extra code pieces:

• tiny fix: remove two spaces in the base64 encoding in <img> tags. Necessary for displaying in jupyter notebooks on github. E.g.
  • old: <img src="data: image/png...
  • new: <img src="data:image/png...
• chore: remove polars map_elements warning by specifying output type

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.72%. Comparing base (d0fe061) to head (7308ea4).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #349 +/- ## ======================================= Coverage 84.72% 84.72% ======================================= Files 41 41 Lines 4346 4346 ======================================= Hits 3682 3682 Misses 664 664 ```

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