(fix): make pipeline pickleable #73

Job	Run time
build sdist	23s
build on linux (x86_64 - 2_28)	3m 52s
build on linux (aarch64 - 2_28)	3m 34s
build on macos (x86_64)	2m 13s
build on macos (aarch64)	2m 10s
build on windows (x86_64)	11m 20s
build on windows (aarch64)	12m 6s
build on linux (armv7 - 2_28)	3m 39s
build on linux (ppc64le - 2_28)	3m 32s
build on linux (x86_64 - musllinux_1_2)	3m 22s
build on linux (aarch64 - musllinux_1_2)	3m 27s
build on linux (armv7 - musllinux_1_2)	3m 25s
build on windows (i686)	11m 11s
inspect	2s
version	0s
publish	0s
	1h 4m 16s

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