Fix GCD and test_int for 60-bit PyLong digits

Two fixes for 60-bit digit support:

1. Fix _PyLong_GCD() to return non-negative results for 60-bit digits
   - The 60-bit path in the "simple" case was skipping long_abs() calls
   - This caused gcd(-1, 0) to return -1 instead of 1
   - Added long_abs() calls for both inputs before the GCD algorithm
   - Fixes test_math::testGcd and all test_pow failures (3,075 cases)

2. Adjust test_pylong_int_divmod_crash for larger digit sizes
   - The test uses k=10,000 to ensure _pylong.int_divmod() is called
   - With 60-bit digits, the threshold is higher (need more bits/digits)
   - Scale k based on bits_per_digit: k = 10,000 * (bits_per_digit // 30)
   - For 60-bit: k=20,000, for 30-bit: k=10,000, for 15-bit: k=5,000

All previously failing tests now pass:
- test_decimal: OK
- test_fractions: OK
- test_int: OK (was 1 failure)
- test_math: OK (was 7 failures)
- test_numeric_tower: OK
- test_pow: OK (was 3,075 failures)
- test_statistics: OK

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: taegyunkim

Lib/test/test_int.py

@@ -784,7 +784,9 @@ def test_pylong_int_divmod_crash(self):
         # Regression test for https://github.com/python/cpython/issues/142554.
         bad_int_divmod = lambda a, b: (1,)
         # 'k' chosen such that divmod(2**(2*k), 2**k) uses _pylong.int_divmod()
-        k = 10_000
+        # Scale k based on digit size: larger digits need larger k to reach the threshold
+        bits_per_digit = sys.int_info.bits_per_digit
+        k = 10_000 * (bits_per_digit // 30)
         a, b = (1 << (2 * k)), (1 << k)
         with mock.patch.object(_pylong, "int_divmod", wraps=bad_int_divmod):
             msg = r"tuple of length 2 is required from int_divmod\(\)"

Objects/longobject.c

@@ -5899,6 +5899,22 @@ _PyLong_GCD(PyObject *aarg, PyObject *barg)
     y = PyLong_AsLongLong((PyObject *)b);
 #else
     /* For very large digits (like 60-bit), fall back to general algorithm */
+    /* First take absolute values, since GCD must be non-negative */
+    PyLongObject *a_abs = long_abs(a);
+    Py_DECREF(a);
+    if (a_abs == NULL) {
+        Py_DECREF(b);
+        return NULL;
+    }
+    PyLongObject *b_abs = long_abs(b);
+    Py_DECREF(b);
+    if (b_abs == NULL) {
+        Py_DECREF(a_abs);
+        return NULL;
+    }
+    a = a_abs;
+    b = b_abs;
+
     /* Use the Euclidean GCD algorithm directly on PyLong objects */
     while (!_PyLong_IsZero(b)) {
         PyLongObject *temp;