Add py free-threaded support #1713

Job	Run time
Build and test with .NET	22s
Build and test cmake:gcc-old	44s
Build and test cmake:package	1m 4s
Build and test cmake:clang	45s
Build and test cmake:static	56s
Build and test cmake:gcc	42s
Build and test cmake:clang-old	51s
Build and test cmake:clang:asan	1m 13s
Build and test cmake-osx:gcc	28s
Build and test cmake:clang:ubsan	1m 6s
Build and test fuzz:clang	49s
Build and test cmake:qemu-arm-neon-gcc	1m 32s
Build and test python3.10:clang	1m 25s
Build and test cmake-ios:clang	34s
Build and test cmake-win64:msvc-rel	1m 5s
Build and test cmake-osx:clang	24s
Build and test bazel:go	1m 28s
Build and test maven	1m 0s
Build and test python3.14:clang	1m 36s
Build and test python3.14t:clang	1m 46s
Build and test bazel:java	2m 21s
Build and test cmake-win64:msvc-dbg	1m 4s
Build and test bazel:research	57s
Build and test python3.14-win	1m 47s
Build and test cmake:clang:tsan	1m 1s
Build and test bazel-osx:root	1m 15s
Build and test bazel-osx:java	4m 1s
Build and test bazel-osx:go	1m 46s
Build and test bazel-win:root	1m 8s
Build and test bazel-win:research	1m 3s
Build and test bazel:root	1m 0s
Build and test bazel-osx:research	1m 5s
	38m 18s

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