refactor: simplify grammar for `in/!in` and `is/!is` #179

Job	Run time
build (ubuntu-20.04, debug)	36s
build (ubuntu-20.04, dev)	37s
build (ubuntu-20.04, release)	1m 32s
build (macos-latest, debug)	1m 10s
build (macos-latest, dev)	1m 25s
build (macos-latest, release)	2m 42s
build (windows-latest, debug)	1m 48s
build (windows-latest, dev)	1m 59s
build (windows-latest, release)	2m 46s
	14m 35s

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