Fix NotImplementedError crash when using xdist schedulers without mark_test_pending (#309)

* Fix NotImplementedError crash when using xdist schedulers without mark_test_pending

Handle gracefully when pytest-xdist schedulers (like LoadScopeScheduling)
don't implement mark_test_pending by catching NotImplementedError and
failing the test with a clear message instead of crashing the test run.

When a test crashes and cannot be rescheduled:
- Set report outcome to "failed" with informative error message
- Explain which scheduler lacks rescheduling support
- Show remaining rerun count that couldn't be used
- Continue test execution instead of internal crash

Fixes #247


---------

Co-authored-by: Michael Howitz <icemac@gmx.net>

Author: msabramo

src/pytest_rerunfailures.py

@@ -361,8 +361,24 @@ def pytest_handlecrashitem(self, crashitem, report, sched):
         db = sched.config.failures_db
         reruns = db.get_test_reruns(crashitem)
         if db.get_test_failures(crashitem) < reruns:
-            sched.mark_test_pending(crashitem)
-            report.outcome = "rerun"
+            try:
+                sched.mark_test_pending(crashitem)
+                report.outcome = "rerun"
+            except NotImplementedError:
+                # Some schedulers (like LoadScopeScheduling) don't implement
+                # mark_test_pending
+                # In this case, we can't reschedule the crashed test for rerun
+                # Mark it as failed with a clear message about why it couldn't be rerun
+                report.outcome = "failed"
+                if not hasattr(report, "longrepr") or report.longrepr is None:
+                    error_msg = (
+                        "Test crashed and could not be rescheduled for rerun."
+                        f" The scheduler '{sched.__class__.__name__}' does not support"
+                        " rescheduling crashed tests"
+                        " (mark_test_pending not implemented)."
+                        f" Remaining reruns: {reruns - db.get_test_failures(crashitem)}"
+                    )
+                    report.longrepr = error_msg
 
         db.add_test_failure(crashitem)