[Not for merge] Optim effects optional #40

Job	Run time
lint-fmt	6m 44s
build (ubuntu-latest, 4.08.x, true, true, true)	7m 38s
build (ubuntu-latest, 4.09.x, true, true, true)	11m 3s
build (ubuntu-latest, 4.10.x, true, true, true)	8m 4s
build (ubuntu-latest, 4.11.x, true, true, true)	7m 28s
build (ubuntu-latest, 4.12.x, true, true, true)	8m 19s
build (ubuntu-latest, 4.13.x, true, true, true)	7m 32s
build (ubuntu-latest, 4.14.x, true, false, true)	15m 0s
build (macos-latest, 4.14.x, true, false, true)	22m 14s
build (windows-latest, 4.14.x, true, false, true)	8m 37s
build (ubuntu-latest, 5.0.x, false, false, false)	13m 19s
build (macos-latest, 5.0.x, true, false, true)	21m 24s
build (windows-latest, ocaml.5.0.0,ocaml-option-mingw, false, false, true)	8m 26s
	2h 25m 48s

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