Add Clippit as an optional comparison engine #16

Job	Run time
build-engine-wheels (ubuntu-latest, linux-x64 linux-arm64)	1m 57s
build-core	15s
build-engine-wheels (windows-latest, win-x64 win-arm64)	2m 21s
build-engine-wheels (macos-latest, osx-x64 osx-arm64)	1m 43s
test (ubuntu-latest, 3.11)	1m 27s
test (ubuntu-latest, 3.9)	1m 30s
test (windows-latest, 3.11)	2m 35s
test (windows-latest, 3.9)	2m 56s
test (ubuntu-latest, 3.12)	1m 26s
test (macos-latest, 3.11)	1m 31s
test (windows-latest, 3.12)	2m 27s
test (macos-latest, 3.12)	1m 21s
test (macos-latest, 3.9)	1m 31s
	23m 0s

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