Use PyFloat_Pack8() on Python 3.11a7 (#499)

Python 3.11a7 adds public functions:

* PyFloat_Pack4(), PyFloat_Pack8()
* PyFloat_Unpack4(), PyFloat_Unpack8()

https://bugs.python.org/issue46906

Author: vstinner

msgpack/pack_template.h

@@ -568,15 +568,24 @@ static inline int msgpack_pack_float(msgpack_packer* x, float d)
 {
     unsigned char buf[5];
     buf[0] = 0xca;
+
+#if PY_VERSION_HEX >= 0x030B00A7
+    PyFloat_Pack4(d, (char *)&buf[1], 0);
+#else
     _PyFloat_Pack4(d, &buf[1], 0);
+#endif
     msgpack_pack_append_buffer(x, buf, 5);
 }
 
 static inline int msgpack_pack_double(msgpack_packer* x, double d)
 {
     unsigned char buf[9];
     buf[0] = 0xcb;
+#if PY_VERSION_HEX >= 0x030B00A7
+    PyFloat_Pack8(d, (char *)&buf[1], 0);
+#else
     _PyFloat_Pack8(d, &buf[1], 0);
+#endif
     msgpack_pack_append_buffer(x, buf, 9);
 }
 

msgpack/unpack_template.h

@@ -243,10 +243,20 @@ static inline int unpack_execute(unpack_context* ctx, const char* data, Py_ssize
                                           _msgpack_load32(uint32_t,n)+1,
                                           _ext_zero);
             case CS_FLOAT: {
-                    double f = _PyFloat_Unpack4((unsigned char*)n, 0);
+                    double f;
+#if PY_VERSION_HEX >= 0x030B00A7
+                    f = PyFloat_Unpack4((const char*)n, 0);
+#else
+                    f = _PyFloat_Unpack4((unsigned char*)n, 0);
+#endif
                     push_fixed_value(_float, f); }
             case CS_DOUBLE: {
-                    double f = _PyFloat_Unpack8((unsigned char*)n, 0);
+                    double f;
+#if PY_VERSION_HEX >= 0x030B00A7
+                    f = PyFloat_Unpack8((const char*)n, 0);
+#else
+                    f = _PyFloat_Unpack8((unsigned char*)n, 0);
+#endif
                     push_fixed_value(_double, f); }
             case CS_UINT_8:
                 push_fixed_value(_uint8, *(uint8_t*)n);