gh-40613: Fix Ctrl-C segfaults in sage.libs.gap
    
Replace cysignals' `sig_on()` and `sig_off()` with custom `gap_sig_on()`
and `gap_sig_off()` wrappers that use GAP's own `SIGINT` handling. This
fixes an uncommon, but ultimately reproducible segfault when Ctrl-C is
used to interrupt a GAP computation.

In concert with #40594 this has
allowed `sage/libs/gap/element.pyx` to pass many thousands of test
iterations.

### Fixes

* #40598

### Dependencies

* #40594
    
URL: #40613
Reported by: Michael Orlitzky
Reviewer(s): Dima Pasechnik, Michael Orlitzky, user202729

Author: Release Manager

src/sage/doctest/util.py

@@ -883,9 +883,16 @@ def ensure_interruptible_after(seconds: float, max_wait_after_interrupt: float =
 
     try:
         yield data
-    except AlarmInterrupt as e:
-        e.__traceback__ = None  # workaround for https://github.com/python/cpython/pull/129276
-        alarm_raised = True
+    except KeyboardInterrupt as e:
+        # AlarmInterrupt is a subclass of KeyboardInterrupt, so this
+        # catches both. The "user interrupt" message is a quirk of
+        # GAP interrupts that result from SIGALRM.
+        if isinstance(e, AlarmInterrupt) or "user interrupt" in str(e):
+            # workaround for https://github.com/python/cpython/pull/129276
+            e.__traceback__ = None
+            alarm_raised = True
+        else:
+            raise
     finally:
         before_cancel_alarm_elapsed = walltime() - start_time
         cancel_alarm()