Update egui from `0.30.0` to `0.31.0` #573

Job	Run time
audit	19s
check (x86_64-unknown-linux-gnu, --all-features --bins)	4m 48s
build (macos-latest, aarch64-apple-darwin)	2m 31s
format	28s
check (wasm32-unknown-unknown, --bin plotinator3000)	55s
build (macos-13, x86_64-apple-darwin, false)	4m 56s
lint	1m 18s
build (ubuntu-latest, aarch64-unknown-linux-gnu, true)	3m 59s
Test Suite (ubuntu-latest)	2m 7s
trunk	1m 27s
build (ubuntu-latest, armv7-unknown-linux-gnueabihf, true)	3m 50s
Test Suite (macos-latest)	2m 9s
build (ubuntu-latest, x86_64-unknown-linux-gnu)	2m 34s
Test Suite (windows-latest)	6m 52s
build (windows-latest, x86_64-pc-windows-msvc, .exe)	7m 36s
tag-release	0s
	45m 49s

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