Calculate stop to subshape mapping during import (#136) #1114

Job	Run time
formatting	44s
macos (macos-x86_64, On)	12m 55s
msvc (Debug)	13m 35s
macos (macos-arm64)	11m 28s
linux (linux-amd64-release, linux-amd64)	29s
msvc (Release)	12m 42s
linux (linux-arm64-release, linux-arm64, qemu-aarch64-static)	35s
linux (clang-tidy)	1m 20s
linux (linux-sanitizer)	2m 13s
linux (linux-debug, valgrind --leak-check=full --error-exitcode=1)	2m 21s
	58m 22s

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