Bump Anthropic.SDK from 5.7.1 to 5.8.0 (#1703)

---
updated-dependencies:
- dependency-name: Anthropic.SDK
  dependency-version: 5.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]

dotnet/Directory.Packages.props

@@ -79,7 +79,7 @@
     <!-- MCP -->
     <PackageVersion Include="ModelContextProtocol" Version="0.4.0-preview.3" />
     <!-- Inference SDKs -->
-    <PackageVersion Include="Anthropic.SDK" Version="5.7.1" />
+    <PackageVersion Include="Anthropic.SDK" Version="5.8.0" />
     <PackageVersion Include="AWSSDK.Extensions.Bedrock.MEAI" Version="4.0.4.1" />
     <PackageVersion Include="Microsoft.ML.OnnxRuntimeGenAI" Version="0.10.0" />
     <PackageVersion Include="OllamaSharp" Version="5.4.8" />