Use the more low-level LazyInitializer to avoid the Lazy<> gotcha

idea from dotnet/runtime#27421 (comment)

src/ProgressOnderwijsUtils/Utils.cs

@@ -27,8 +27,15 @@ public static bool FuzzyEquals(double x, double y)
             return x == y || delta / magnitude < relativeEpsilon;
         }
 
-        public static Lazy<T> Lazy<T>(Func<T> factory)
-            => new Lazy<T>(factory, LazyThreadSafetyMode.ExecutionAndPublication);
+        public static Func<T> Lazy<T>(Func<T> factory)
+        {
+            //Ideally we'd use Lazy<T>, but that either caches exceptions or fails to lock around initialization. see: https://github.com/dotnet/runtime/issues/27421#issuecomment-424732179
+            var value = default(T?);
+            var initialized = false;
+            var sync = (object)factory;
+
+            return () => LazyInitializer.EnsureInitialized(ref value, ref initialized, ref sync, factory);
+        }
 
         /// <summary>
         /// Swap two objects.

test/ProgressOnderwijsUtils.Tests/UtilsTest.cs

@@ -92,14 +92,14 @@ public void LazyRetriesExceptions()
             var sometimesFailingLazy = Utils.Lazy(() => ++count % 4 == 0 ? count : throw new("gotcha!"));
 
             PAssert.That(() => count == 1);
-            PAssert.That(() => nonFailingLazy.Value == 2);
+            PAssert.That(() => nonFailingLazy() == 2);
             PAssert.That(() => count == 2);
-            PAssert.That(() => nonFailingLazy.Value == 2, "A second read of the lazily computed value should not change the value");
+            PAssert.That(() => nonFailingLazy() == 2, "A second read of the lazily computed value should not change the value");
             PAssert.That(() => count == 2, "A second read of the lazily computed value must not have side-effects");
 
-            _ = Assert.Throws<Exception>(() => _ = sometimesFailingLazy.Value);
+            _ = Assert.Throws<Exception>(() => _ = sometimesFailingLazy());
             PAssert.That(() => count == 3);
-            PAssert.That(() => sometimesFailingLazy.Value == 4);
+            PAssert.That(() => sometimesFailingLazy() == 4);
         }
 
         [Fact]