tests: scale memory_ipc outer timeout with child_timeout_sec

Replace the fixed 300 s pytest.mark.timeout with 3 * child_timeout_sec().
This is the minimum that lets the worst-case test in the suite (currently
TestIpcReexport, with three sequential CHILD_TIMEOUT_SEC waits in the
failure path) reach its own asserts before the outer guard fires.

Resulting budgets:
- Without compute-sanitizer: 90 s (down from 300 s).
- Under compute-sanitizer:  360 s (up from 300 s -- the previous value
  would have killed TestIpcReexport mid-second-join before its
  "process C did not signal completion within timeout" assertion could
  produce a clean failure message).

The meta-test test_outer_timeout_marker_is_applied now computes the
expected timeout from the same formula so the two stay in sync.

Author: Andy-Jost

cuda_core/tests/memory_ipc/conftest.py

@@ -13,13 +13,23 @@
 import pathlib
 
 import pytest
+from helpers.child_processes import child_timeout_sec
 
 _HERE = pathlib.Path(__file__).parent.resolve()
-_TIMEOUT_SEC = 300  # 5 minutes per test; generous compared to child_timeout_sec().
+
+
+def _outer_timeout_sec() -> int:
+    # The worst-case IPC test has three sequential CHILD_TIMEOUT_SEC waits in
+    # the failure path (e.g. TestIpcReexport: event_c.wait, proc_b.join,
+    # proc_c.join). Scaling by 3 lets such a test reach its own asserts before
+    # the outer guard fires, while still cutting the budget by half on
+    # non-sanitizer runs (90 s vs the previous 300 s) and scaling up under
+    # compute-sanitizer (360 s).
+    return 3 * child_timeout_sec()
 
 
 def pytest_collection_modifyitems(config, items):
-    marker = pytest.mark.timeout(_TIMEOUT_SEC)
+    marker = pytest.mark.timeout(_outer_timeout_sec())
     for item in items:
         try:
             item_path = pathlib.Path(str(item.fspath)).resolve()

cuda_core/tests/memory_ipc/test_errors.py

@@ -25,9 +25,10 @@ def test_outer_timeout_marker_is_applied(request):
     the in-test cleanup -- which we want to keep as defense in depth, not as
     the sole guard.
     """
+    expected = 3 * child_timeout_sec()
     marker = request.node.get_closest_marker("timeout")
     assert marker is not None, "memory_ipc/conftest.py did not apply a timeout marker"
-    assert marker.args == (300,), f"unexpected timeout value: {marker.args!r}"
+    assert marker.args == (expected,), f"unexpected timeout value: {marker.args!r}"
 
 
 class ChildErrorHarness: