Add CFFI thread safety docs #431

Job	Run time
python_sdist	10s
make_linux_matrix	5s
make_windows_matrix	5s
make_macos_matrix	4s
clang_TSAN	4m 23s
make_run_parallel_matrix	4s
pytest-run-parallel (ubuntu-latest, 3.14t-dev)	4m 38s
pytest-run-parallel (windows-latest, 3.14t-dev)	2m 4s
pytest-run-parallel (macos-latest, 3.14t-dev)	5m 19s
macos (cp314-macosx_x86_64, macos-13)	9m 56s
macos (cp314t-macosx_arm64, 11.0, arch -arm64 bash --noprofile --norc -eo pipefail {0})	5m 7s
macos (cp314-macosx_arm64, 11.0, arch -arm64 bash --noprofile --norc -eo pipefail {0})	4m 59s
macos (cp314t-macosx_x86_64, macos-13)	8m 47s
linux (cp314t-manylinux_x86_64, x86_64)	4m 58s
linux (cp314-manylinux_x86_64, x86_64)	4m 44s
linux (cp314-musllinux_x86_64, x86_64)	5m 48s
linux (cp313-manylinux_i686, i686)	5m 21s
linux (cp311-musllinux_i686, i686)	5m 8s
linux (cp314t-manylinux_aarch64, aarch64)	4m 48s
linux (cp314-manylinux_aarch64, aarch64)	4m 31s
linux (cp39-manylinux_aarch64, aarch64)	4m 25s
linux (cp314-musllinux_aarch64, aarch64)	4m 35s
linux (cp314t-musllinux_aarch64, aarch64)	5m 18s
linux (cp314t-musllinux_x86_64, x86_64)	6m 13s
windows (cp314-win32)	1m 54s
windows (cp314t-win32)	1m 51s
windows (cp314-win_amd64)	1m 26s
windows (cp314t-win_amd64)	1m 19s
windows (cp314-win_arm64, windows-11-arm)	2m 8s
windows (cp314t-win_arm64, windows-11-arm)	3m 24s
merge_artifacts	4s
check	2s
	1h 53m 38s

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