feat: add Violin trace type #220

Job	Run time
Rustfmt	13s
semver	59s
Build Wasm Examples (basic)	59s
Clippy	5m 35s
Tests (windows-latest, chrome, plotly_ndarray,plotly_image,static_export_chromedriver,debug)	8m 18s
Build Wasm Examples (callback-example)	1m 2s
Build Book	4m 17s
Code Coverage	18s
Tests (ubuntu-latest, firefox, plotly_ndarray,plotly_image,static_export_geckodriver,static_expor...	3m 16s
Tests (ubuntu-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	3m 9s
Build Examples (custom_controls)	36s
Build Examples (customization/density_mapbox_example)	31s
Build Examples (themes)	38s
Build Examples (subplots)	34s
Build Examples (financial_charts)	32s
Build Examples (basic_charts)	36s
Build Examples (customization/consistent_static_format_export)	1m 50s
Tests (macos-latest, chrome, plotly_ndarray,plotly_image,static_export_default,debug)	3m 16s
Build Examples (shapes)	37s
Build Examples (kaleido)	1m 32s
Build Examples (customization/multiple_plots_example)	35s
Build Examples (statistical_charts)	39s
Build Examples (images)	54s
Build Examples (scientific_charts)	34s
Build Examples (maps)	42s
Build Examples (ndarray)	35s
Build Examples (3d_charts)	36s
	43m 23s

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