Py runtime: Move to relative imports #1135

Job	Run time
cpp-lib-build (macos-12, clang, ON)	1s
cpp-lib-build (macos-12, clang, OFF)	1s
build (macos-12, tool)	1s
cpp-lib-build (macos-12, gcc, ON)	1s
build (macos-12, cpp)	1m 26s
cpp-lib-build (macos-12, gcc, OFF)	1s
build (macos-12, csharp)	1m 15s
cpp-lib-build (ubuntu-20.04, clang, ON)	1s
build (macos-12, dart)	1m 6s
build (macos-12, go)	1m 14s
cpp-lib-build (ubuntu-20.04, clang, OFF)	1s
build (macos-12, java)	1m 21s
cpp-lib-build (ubuntu-20.04, gcc, ON)	1s
build (macos-12, javascript)	1s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	1s
build (macos-12, typescript)	1s
cpp-lib-build (windows-2022, clang, ON)	1s
build (macos-12, php)	1s
cpp-lib-build (windows-2022, clang, OFF)	1s
build (macos-12, python3)	1s
cpp-lib-build (windows-2022, cl)	1s
build (ubuntu-20.04, tool)	1m 9s
build (ubuntu-20.04, cpp)	1m 27s
build (ubuntu-20.04, csharp)	1m 25s
build (ubuntu-20.04, dart)	1m 15s
build (ubuntu-20.04, go)	1m 25s
build (ubuntu-20.04, java)	1m 16s
build (ubuntu-20.04, javascript)	1m 12s
build (ubuntu-20.04, typescript)	1m 35s
build (ubuntu-20.04, php)	1m 6s
build (ubuntu-20.04, python3)	1m 0s
build (windows-2022, tool)	1s
build (windows-2022, cpp)	59s
build (windows-2022, csharp)	1m 2s
build (windows-2022, dart)	1m 4s
build (windows-2022, go)	1m 3s
build (windows-2022, java)	1m 3s
build (windows-2022, javascript)	1s
build (windows-2022, typescript)	1s
build (windows-2022, php)	1s
build (windows-2022, python3)	1s
	24m 44s

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