Added `platypus` theme #2191

Job	Run time
Code coverage	3m 11s
Clippy	51s
Integration tests (macos-latest)	1m 53s
Integration tests (ubuntu-latest)	2m 29s
Rustfmt	10s
Unit tests (macos-latest, aarch64-apple-darwin, false)	2m 31s
Unit tests (macos-12, x86_64-apple-darwin, false)	4m 25s
Unit tests (windows-latest, x86_64-pc-windows-msvc, false)	5m 0s
Unit tests (ubuntu-latest, x86_64-unknown-linux-gnu, false)	2m 33s
Unit tests (ubuntu-latest, x86_64-unknown-linux-musl, true)	3m 7s
Unit tests (ubuntu-latest, i686-unknown-linux-gnu, true)	3m 21s
Unit tests (ubuntu-latest, arm-unknown-linux-gnueabihf, true)	3m 22s
Unit tests (ubuntu-latest, aarch64-unknown-linux-gnu, true)	3m 4s
	35m 57s

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