Add py free-threaded support #1709

Job	Run time
Build and test with .NET	23s
Build and test cmake:gcc	43s
Build and test cmake-osx:clang	27s
Build and test cmake:clang:asan	56s
Build and test cmake:package	1m 1s
Build and test cmake-win64:msvc-dbg	42s
Build and test python3.10:clang	53s
Build and test cmake:clang-old	45s
Build and test cmake:static	54s
Build and test cmake:clang:tsan	1m 10s
Build and test maven	50s
Build and test cmake-win64:msvc-rel	43s
Build and test cmake:clang:ubsan	1m 7s
Build and test cmake:gcc-old	44s
Build and test bazel-osx:java	2m 46s
Build and test python3.14-win	1m 7s
Build and test bazel-osx:research	47s
Build and test cmake:qemu-arm-neon-gcc	1m 26s
Build and test fuzz:clang	57s
Build and test python3.14:clang	47s
Build and test cmake-ios:clang	29s
Build and test cmake:clang	44s
Build and test bazel-osx:root	1m 9s
Build and test cmake-osx:gcc	39s
Build and test python3.14t:clang	58s
Build and test bazel:research	36s
Build and test bazel:java	2m 20s
Build and test bazel-win:root	1m 16s
Build and test bazel:go	1m 21s
Build and test bazel-win:research	1m 12s
Build and test bazel:root	52s
Build and test bazel-osx:go	1m 38s
	32m 22s

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