test the custom signal handler with cypari2

This test triggers the following bug on cysignals 1.12.0 - 1.12.2:

```
Python 3.13.1 (main, Dec 14 2024, 12:44:03) [GCC 13.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cypari2
>>> from cysignals.alarm import alarm
>>> try:
...     alarm(0.5)
...     while True: pass
... except:
...     pass
...
>>> cypari2.Pari()
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    cypari2.Pari()
    ~~~~~~~~~~~~^^
  File "cypari2/pari_instance.pyx", line 471, in cypari2.pari_instance.Pari.__cinit__
  File "cypari2/closure.pyx", line 138, in cypari2.closure._pari_init_closure
cysignals.signals.AlarmInterrupt
```

Author: tornaria

pyproject.toml

@@ -34,4 +34,4 @@ requires-python = ">=3.9"
 
 [tool.pytest.ini_options]
 addopts = "--doctest-modules --import-mode importlib"
-norecursedirs = "builddir docs example"
+testpaths = "src tests"

tests/test_custom_signals.py

@@ -0,0 +1,17 @@
+import pytest
+import time
+
+def test_clear_pending():
+
+    from cysignals.alarm import alarm, AlarmInterrupt
+
+    cypari2 = pytest.importorskip("cypari2")
+
+    with pytest.raises(AlarmInterrupt):
+        alarm(0.5)
+        time.sleep(1)
+
+    try:
+        cypari2.Pari()
+    except AlarmInterrupt:
+        pytest.fail("AlarmInterrupt was not cleared")