.NET: Update A2A, MCP, and system package dependencies (#4647)
* .NET: Update A2A, MCP, and system package dependencies
Update dependency versions:
- A2A/A2A.AspNetCore: 0.3.3-preview → 0.3.4-preview
- ModelContextProtocol: 0.8.0-preview.1 → 1.1.0
- Microsoft.Bcl.AsyncInterfaces: 10.0.3 → 10.0.4
- System.Linq.AsyncEnumerable: 10.0.0 → 10.0.4
- Add Microsoft.Bcl.Memory 10.0.4
Remove internal polyfill extensions now provided by A2A SDK 0.3.4:
- A2AMetadataExtensions (source + tests)
- AdditionalPropertiesDictionaryExtensions (source + tests)
Update DefaultMcpToolHandler to match MCP SDK 1.1.0 API changes where
ImageContentBlock.Data and AudioContentBlock.Data changed from string
to ReadOnlyMemory<byte>.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
* address pr review comments
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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>