The `barchart` example has been split into two examples: `barchart` and
`barchart-grouped`. The `barchart` example now shows a simple barchart
with random data, while the `barchart-grouped` example shows a grouped
barchart with fake revenue data.
This simplifies the examples a bit so they don't cover too much at once.
- Simplify the rendering functions
- Fix several clippy lints that were marked as allowed
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Co-authored-by: EdJoPaTo <rfc-conform-git-commit-email@funny-long-domain-label-everyone-hates-as-it-is-too-long.edjopato.de>
