Pydantic AI v2.19.0 adds HTTP error metadata and FastMCP 4 support

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Pydantic AI — a Python agent framework built around Pydantic's data validation — released v2.19.0 on July 27, 2026. The main feature adds headers and retry_after fields to ModelHTTPError, populated automatically across all provider SDKs, making it easier for agents to handle rate-limit responses gracefully without custom parsing. The release also widens the FastMCP (a Model Context Protocol server library) dependency range to support up to version 4, keeping compatibility with the latest MCP tooling.