Add a `ScrollView` and refactor painting logic with a newly added `Ca… #51

Job	Run time
cargo fmt	15s
cargo clippy + test (windows-latest)	1m 5s
cargo doc (windows-latest)	39s
cargo clippy + test (macos-latest)	1m 2s
cargo doc (macos-latest)	25s
cargo clippy + test (ubuntu-latest)	31s
cargo doc (ubuntu-latest)	19s
	4m 16s

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