Add py free-threaded support #1714

Job	Run time
Build and test with .NET	20s
Build and test cmake:clang	46s
Build and test cmake:gcc	1m 12s
Build and test cmake:clang-old	43s
Build and test cmake:clang:tsan	1m 1s
Build and test cmake-osx:clang	1m 49s
Build and test fuzz:clang	53s
Build and test python3.14:clang	1m 37s
Build and test bazel:root	53s
Build and test python3.14-win	1m 47s
Build and test maven	1m 7s
Build and test cmake-osx:gcc	35s
Build and test python3.10:clang	1m 19s
Build and test cmake-ios:clang	32s
Build and test cmake:qemu-arm-neon-gcc	1m 15s
Build and test bazel:go	1m 19s
Build and test cmake:package	1m 4s
Build and test python3.14t:clang	1m 49s
Build and test bazel:research	42s
Build and test cmake:clang:ubsan	1m 2s
Build and test cmake-win64:msvc-dbg	41s
Build and test bazel-osx:research	1m 11s
Build and test bazel:java	2m 20s
Build and test cmake:static	45s
Build and test bazel-osx:go	1m 32s
Build and test cmake:gcc-old	42s
Build and test bazel-osx:root	1m 27s
Build and test cmake-win64:msvc-rel	45s
Build and test bazel-win:research	1m 7s
Build and test bazel-osx:java	3m 4s
Build and test bazel-win:root	1m 24s
Build and test cmake:clang:asan	55s
	37m 38s

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