Py runtime: Move to relative imports #1136

Job	Run time
cpp-lib-build (macos-12, clang, ON)	51s
build (macos-12, tool)	1m 30s
cpp-lib-build (macos-12, clang, OFF)	1m 29s
build (macos-12, cpp)	12m 55s
cpp-lib-build (macos-12, gcc, ON)	55s
build (macos-12, csharp)	6m 23s
cpp-lib-build (macos-12, gcc, OFF)	1m 31s
build (macos-12, dart)	3m 51s
cpp-lib-build (ubuntu-20.04, clang, ON)	58s
build (macos-12, go)	3m 7s
cpp-lib-build (ubuntu-20.04, clang, OFF)	1m 11s
build (macos-12, java)	1m 43s
cpp-lib-build (ubuntu-20.04, gcc, ON)	2m 9s
build (macos-12, javascript)	2m 6s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	2m 15s
build (macos-12, typescript)	15m 36s
cpp-lib-build (windows-2022, clang, ON)	4m 5s
build (macos-12, php)	28m 8s
cpp-lib-build (windows-2022, clang, OFF)	5m 16s
build (macos-12, python3)	1m 47s
cpp-lib-build (windows-2022, cl)	4m 12s
build (ubuntu-20.04, tool)	57s
build (ubuntu-20.04, cpp)	16m 4s
build (ubuntu-20.04, csharp)	5m 34s
build (ubuntu-20.04, dart)	3m 37s
build (ubuntu-20.04, go)	2m 39s
build (ubuntu-20.04, java)	1m 7s
build (ubuntu-20.04, javascript)	1m 21s
build (ubuntu-20.04, typescript)	10m 12s
build (ubuntu-20.04, php)	1m 35s
build (ubuntu-20.04, python3)	1m 4s
build (windows-2022, tool)	1m 32s
build (windows-2022, cpp)	23m 32s
build (windows-2022, csharp)	6m 42s
build (windows-2022, dart)	4m 9s
build (windows-2022, go)	5m 46s
build (windows-2022, java)	1m 47s
build (windows-2022, javascript)	2m 32s
build (windows-2022, typescript)	21m 0s
build (windows-2022, php)	2m 23s
build (windows-2022, python3)	1m 40s
	3h 37m 11s

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