fix: FilterOutFutureInstant should not filter out all non-Instant components

src/Nitride.Temporal/FilterOutFutureInstant.cs

@@ -25,9 +25,11 @@ public partial class FilterOutFutureInstant : OperationBase
     {
         Instant now = this.Timekeeper.Clock.GetCurrentInstant();
 
-        return input.WhereEntity<Instant>(
+        return input
+            .SelectEntity<Instant>(
                 (
-                _,
-                instant) => instant.CompareTo(now) <= 0);
+                        entity,
+                        instant) =>
+                    instant.CompareTo(now) <= 0 ? entity : null);
     }
 }

tests/Nitride.Temporal.Tests/FilterOutFutureInstantTests.cs

@@ -46,4 +46,33 @@ public class FilterOutFutureInstantTests : TemporalTestBase
         Entity entity = Assert.Single(output);
         Assert.Equal("past", entity.Get<string>());
     }
+
+    [Fact]
+    public void KeepsNonInstant()
+    {
+        // Create the context and set the timestamp to a constant value.
+        using TemporalTestContext context = this.CreateContext();
+        Timekeeper timekeeper = context.Resolve<Timekeeper>();
+        var now = Instant.FromUtc(2000, 6, 1, 0, 0);
+
+        timekeeper.Clock = new FakeClock(now);
+
+        // Create the entities.
+        List<Entity> input = new()
+        {
+            new Entity()
+                .Add("neither"),
+            new Entity()
+                .Add("future")
+                .Add(Instant.FromUtc(2020, 6, 1, 0, 0)),
+        };
+
+        // Create the operation and run it.
+        FilterOutFutureInstant op = context.Resolve<FilterOutFutureInstant>();
+        IEnumerable<Entity> output = input.Run(op);
+
+        // Verify the values.
+        Entity entity = Assert.Single(output);
+        Assert.Equal("neither", entity.Get<string>());
+    }
 }