Add channel test providers for Email, Slack, Teams, and Webhook

- Implemented EmailChannelTestProvider to generate email preview payloads.
- Implemented SlackChannelTestProvider to create Slack message previews.
- Implemented TeamsChannelTestProvider for generating Teams Adaptive Card previews.
- Implemented WebhookChannelTestProvider to create webhook payloads.
- Added INotifyChannelTestProvider interface for channel-specific preview generation.
- Created ChannelTestPreviewContracts for request and response models.
- Developed NotifyChannelTestService to handle test send requests and generate previews.
- Added rate limit policies for test sends and delivery history.
- Implemented unit tests for service registration and binding.
- Updated project files to include necessary dependencies and configurations.

src/StellaOps.Concelier.Exporter.Json.Tests/JsonExportSnapshotBuilderTests.cs

@@ -42,10 +42,14 @@ public sealed class JsonExportSnapshotBuilderTests : IDisposable
                 severity: "medium"),
         };
 
-        var result = await builder.WriteAsync(advisories, exportedAt, cancellationToken: CancellationToken.None);
-
-        Assert.Equal(advisories.Length, result.AdvisoryCount);
-        Assert.Equal(exportedAt, result.ExportedAt);
+        var result = await builder.WriteAsync(advisories, exportedAt, cancellationToken: CancellationToken.None);
+
+        Assert.Equal(advisories.Length, result.AdvisoryCount);
+        Assert.Equal(advisories.Length, result.Advisories.Length);
+        Assert.Equal(
+            advisories.Select(a => a.AdvisoryKey).OrderBy(key => key, StringComparer.Ordinal),
+            result.Advisories.Select(a => a.AdvisoryKey).OrderBy(key => key, StringComparer.Ordinal));
+        Assert.Equal(exportedAt, result.ExportedAt);
 
         var expectedFiles = result.FilePaths.OrderBy(x => x, StringComparer.Ordinal).ToArray();
         Assert.Contains("nvd/2024/CVE-2024-9999.json", expectedFiles);
@@ -107,10 +111,11 @@ public sealed class JsonExportSnapshotBuilderTests : IDisposable
         };
 
         var sequence = new SingleEnumerationAsyncSequence(advisories);
-        var result = await builder.WriteAsync(sequence, exportedAt, cancellationToken: CancellationToken.None);
-
-        Assert.Equal(advisories.Length, result.AdvisoryCount);
-    }
+        var result = await builder.WriteAsync(sequence, exportedAt, cancellationToken: CancellationToken.None);
+
+        Assert.Equal(advisories.Length, result.AdvisoryCount);
+        Assert.Equal(advisories.Length, result.Advisories.Length);
+    }
 
     private static Advisory CreateAdvisory(string advisoryKey, string[] aliases, string title, string severity)
     {