Update the interface for declaring Python download preferences #412

Job	Run time
macos-x86_64	9m 52s
macos-aarch64	5m 56s
windows (x86_64-pc-windows-msvc, x64)	12m 28s
sdist	7m 16s
windows (i686-pc-windows-msvc, x86)	12m 27s
linux (x86_64-unknown-linux-gnu)	8m 7s
linux (i686-unknown-linux-gnu)	11m 14s
linux-arm (aarch64-unknown-linux-gnu, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	8m 27s
linux-powerpc (powerpc64le-unknown-linux-gnu, ppc64le)	8m 46s
linux-arm (armv7-unknown-linux-gnueabihf, armv7)	7m 52s
linux-s390x (s390x-unknown-linux-gnu, s390x)	12m 2s
linux-arm (arm-unknown-linux-musleabihf, arm)	7m 33s
linux-powerpc (powerpc64-unknown-linux-gnu, ppc64)	8m 52s
musllinux (x86_64-unknown-linux-musl)	7m 55s
musllinux (i686-unknown-linux-musl)	7m 46s
musllinux-cross (aarch64-unknown-linux-musl, aarch64, -e JEMALLOC_SYS_WITH_LG_PAGE=16)	4m 8s
musllinux-cross (armv7-unknown-linux-musleabihf, armv7)	4m 7s
musllinux-cross (powerpc64le-unknown-linux-musl, ppc64le, nightly)	4m 5s
	2h 28m 53s

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