Release transient SYCL queues at the end of each test file to avoid OOM on low-memory GPUs (#3001)

Running the full test suite in a single process steadily drains device
memory and can end in a `RuntimeError: ...
UR_RESULT_ERROR_OUT_OF_RESOURCES` (seen intermittently on a low-memory
iGPU, where the kernel logs `VM worker error: -12` / `exec queue reset
detected`).

Root cause: every distinct `dpctl.SyclQueue` a test creates is retained
**for the whole session** as a key in dpctl's `SequentialOrderManager`
(the map is keyed by queue identity and only ever grows). Each retained
entry holds a host-task event that pins the backing USM allocation, so
the memory is never released. Over a full run the map accumulates ~300
queues
and free device memory bleeds from several GB down to ~1 GB,
occasionally crossing the device limit.

This is amplified on integrated GPUs, where "device memory" is system
RAM, so the leaked USM competes directly with the host and the
container's memory budget.

Author: antonwolfy

dpnp/tests/conftest.py

@@ -31,6 +31,7 @@
 import warnings
 
 import dpctl
+import dpctl.utils as dpu
 import numpy
 import pytest
 
@@ -186,6 +187,27 @@ def pytest_collection_modifyitems(config, items):
                 item.add_marker(skip_slow)
 
 
+def pytest_runtest_teardown(item, nextitem):
+    """
+    Release transient SYCL queues at the end of each test file.
+
+    Every distinct ``SyclQueue`` a test creates is retained forever as a key in
+    dpctl's ``SequentialOrderManager`` (keyed by queue identity), which pins its
+    host-task events and the backing USM memory for the whole session. Over a
+    full run this accumulates hundreds of queues and steadily drains device
+    memory. Draining and dropping them at each file boundary keeps the footprint
+    flat without paying the cost after every individual test.
+    """
+    # Only act on the last test of the current file (``nextitem`` is None at the
+    # very end of the session, or points at the first test of the next file).
+    if nextitem is not None and item.path == nextitem.path:
+        return
+    try:
+        dpu.SequentialOrderManager.clear()
+    except Exception as e:  # never let cleanup break the run
+        warnings.warn(f"Failed to clear SequentialOrderManager: {e}")
+
+
 @pytest.fixture
 def allow_fall_back_on_numpy(monkeypatch):
     monkeypatch.setattr(