0.30.0

Full diff at https://github.com/emilk/egui_plot/compare/0.29.0..HEAD

PRs

• Update to egui 0.30.0, MSRV to 1.80 #59 by @bircni
• Allow setting a line's fill area's alpha channel #34 by @maxded
• Use Vec2b in parameters #43 by @bircni
• Fix axis thickness for multiple X or Y axes #60 by @raymanfx
• Fix axis labels overlap with axis ticks #57 by @mkalte666
• Add PlotUi::add_item(Box<dyn PlotItem>) #51 by @freeformstu
• Implement custom ruler color for Plot #47 by @gweisert