Build free-threaded wheels, disable limited API there

Co-authored-by: Min RK <151929+minrk@users.noreply.github.com>

.github/workflows/wheels.yml

@@ -39,12 +39,14 @@ jobs:
       - uses: pypa/cibuildwheel@v2.21.2
         env:
           # Only build CPython 3.9, because we have portable abi3 wheels.
-          CIBW_BUILD: "cp39-* cp39-win_arm64"
+          # Only exception are free-threaded builds.
+          CIBW_BUILD: "cp39-* cp39-win_arm64 cp313t-*"
           CIBW_ARCHS_LINUX: "auto aarch64"
           CIBW_ARCHS_MACOS: "auto universal2"
           CIBW_TEST_COMMAND: python -Ic "from _argon2_cffi_bindings import ffi, lib; print(lib.ARGON2_VERSION_NUMBER)"
           # https://github.com/pypa/cibuildwheel/pull/1169
           CIBW_TEST_SKIP: "*-macosx_universal2:arm64"
+          CIBW_FREE_THREADED_SUPPORT: true
 
       - uses: actions/upload-artifact@v4
         with:

setup.py

@@ -2,6 +2,7 @@
 
 import platform
 import sys
+import sysconfig
 
 from setuptools import setup
 
@@ -17,7 +18,11 @@
 
         class BDistWheel(bdist_wheel):
             def finalize_options(self):
-                self.py_limited_api = f"cp3{sys.version_info[1]}"
+                # Free-threaded CPython doesn't support limited API.
+                if sysconfig.get_config_var("Py_GIL_DISABLED"):
+                    self.py_limited_api = False
+                else:
+                    self.py_limited_api = f"cp3{sys.version_info[1]}"
 
                 super().finalize_options()
 

src/_argon2_cffi_bindings/_ffi_build.py

@@ -2,6 +2,7 @@
 
 import os
 import platform
+import sysconfig
 
 from pathlib import Path
 
@@ -11,6 +12,8 @@
 use_system_argon2 = os.environ.get("ARGON2_CFFI_USE_SYSTEM", "0") == "1"
 use_sse2 = os.environ.get("ARGON2_CFFI_USE_SSE2", None)
 windows = platform.system() == "Windows"
+# Free-threaded CPython doesn't support limited API.
+limited_api = not sysconfig.get_config_var("Py_GIL_DISABLED")
 
 
 # Try to detect cross-compilation.
@@ -48,6 +51,7 @@ def _get_target_platform(arch_flags, default):
         "_ffi",
         "#include <argon2.h>",
         libraries=["argon2"],
+        py_limited_api=limited_api,
     )
 else:
     lib_base = Path("extras") / "libargon2" / "src"
@@ -56,6 +60,7 @@ def _get_target_platform(arch_flags, default):
         "#include <argon2.h>",
         extra_compile_args=["-msse2"] if (optimized and not windows) else None,
         include_dirs=[os.path.join("extras", "libargon2", "include")],
+        py_limited_api=limited_api,
         sources=[
             str(lib_base / path)
             for path in [