Using calculus to improve accuracy of `atan`. #350

Job	Run time
build (ubuntu-latest, Release, clang, 3.10)	4m 40s
build (ubuntu-latest, Release, clang, 3.11)	4m 36s
build (ubuntu-latest, Release, clang, 3.12)	4m 42s
build (windows-2019, Release, cl, 3.10)	5m 0s
build (windows-2019, Release, cl, 3.11)	5m 45s
build (windows-2019, Release, cl, 3.12)	5m 46s
build (macos-12, Release, clang, 3.10)	3m 30s
build (macos-12, Release, clang, 3.11)	3m 17s
build (macos-12, Release, clang, 3.12)	3m 1s
build (macos-13, Release, clang, 3.10)	3m 3s
build (macos-13, Release, clang, 3.11)	3m 5s
build (macos-13, Release, clang, 3.12)	3m 5s
build (macos-14, Release, clang, 3.10)	1m 37s
build (macos-14, Release, clang, 3.11)	1m 32s
build (macos-14, Release, clang, 3.12)	1m 31s
	54m 10s

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