fix(test): mark large memory tests as [OpenBugs] for CI exclusion

AllocationTests and LongIndexingBroadcastTest cause OOM crashes on CI
runners. Marking them as [OpenBugs] excludes them via the existing
--treenode-filter in the CI workflow.

Changes:
- Added [OpenBugs] to AllocationTests class (4 tests allocating 4-44GB)
- Added [OpenBugs] to LongIndexingBroadcastTest class (25 tests iterating 2.36B elements)
- Removed [SkipOnLowMemory] infrastructure (attribute, tracker, hook)

These tests can still be run locally on machines with sufficient memory
by running without the OpenBugs filter.

Author: Nucs

test/NumSharp.UnitTest/Backends/Unmanaged/AllocationTests.cs

@@ -2,24 +2,22 @@
 using AwesomeAssertions;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using NumSharp.Backends;
-using NumSharp.UnitTest.Utilities;
 
 namespace NumSharp.UnitTest.Backends.Unmanaged
 {
     /// <summary>
     /// Tests for large memory allocations.
-    /// Marked as [HighMemory] because they allocate 1-4GB of memory and
-    /// can cause OOM on CI runners (especially ubuntu with limited RAM).
+    /// Marked as [OpenBugs] because they allocate 4-44GB of memory and
+    /// cause OOM crashes on CI runners.
     /// </summary>
     [HighMemory]
+    [OpenBugs]
     public class AllocationTests
     {
         private const long onegb = 1_073_741_824;
         private static readonly object _lock = new Object();
 
         [Test]
-        [HighMemory]
-        [SkipOnLowMemory(8)] // Actually allocates 4GB (Int32 * 1B elements)
         public void Allocate_1GB()
         {
             lock (_lock)
@@ -31,8 +29,6 @@ public void Allocate_1GB()
         }
 
         [Test]
-        [HighMemory]
-        [SkipOnLowMemory(12)] // Actually allocates 8GB (Int32 * 2B elements)
         public void Allocate_2GB()
         {
             lock (_lock)
@@ -44,8 +40,6 @@ public void Allocate_2GB()
         }
 
         [Test]
-        [HighMemory]
-        [SkipOnLowMemory(20)] // Actually allocates 16GB (Int32 * 4B elements)
         public void Allocate_4GB()
         {
             lock (_lock)
@@ -57,9 +51,6 @@ public void Allocate_4GB()
         }
 
         [Test]
-        [HighMemory]
-        [SkipOnLowMemory(50)] // Actually allocates 44GB+
-        [OpenBugs]
         public void Allocate_44GB()
         {
             lock (_lock)

test/NumSharp.UnitTest/LongIndexing/LongIndexingBroadcastTest.cs

@@ -2,7 +2,6 @@
 using System.Threading.Tasks;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using NumSharp;
-using NumSharp.UnitTest.Utilities;
 using TUnit.Core;
 
 namespace NumSharp.UnitTest.LongIndexing;
@@ -22,12 +21,12 @@ namespace NumSharp.UnitTest.LongIndexing;
 /// - Operations that produce output (add, multiply, etc.) allocate full-size output arrays
 ///   even when input is broadcast, causing OutOfMemoryException
 ///
-/// NOTE: Marked [HighMemory] because iterating over 2.36 billion elements causes
+/// NOTE: Marked [OpenBugs] because iterating over 2.36 billion elements causes
 /// excessive CPU/memory pressure when TUnit runs tests in parallel, leading to
-/// OOM kills on Ubuntu CI runners.
+/// OOM crashes on CI runners.
 /// </summary>
 [HighMemory]
-[SkipOnLowMemory(12)] // Skip on CI runners with limited memory
+[OpenBugs]
 public class LongIndexingBroadcastTest
 {
     /// <summary>