feat(spec): Update A2A types from specification 🤖

[a2a-bot]

This PR updates src/a2a/types.py based on the latest specification/json/a2a.json from a2aproject/A2A.

[gemini-code-assist]

Summary of Changes

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This pull request, automatically generated by a2a-bot, updates the A2A Python types in src/a2a/types.py to align with the latest A2A specification. The primary focus of these changes is to enhance the definition and validation of URLs and transport protocols within the A2A models, providing clearer guidance and more robust data structures for agent interfaces.

Highlights

• Type Enhancements for URLs: The url fields within the AgentInterface and AgentCard models have been upgraded from str to pydantic.AnyUrl. This change introduces robust URL validation and improves type safety, ensuring that all URLs conform to a valid format.
• Formalized Transport Protocols: A new TransportProtocol Enum has been introduced. This enum explicitly defines the core supported A2A transport protocols (JSONRPC, GRPC, HTTP+JSON), enhancing clarity, consistency, and maintainability when referencing these protocols.
• Improved Agent Interface and Card Definitions: The AgentInterface and AgentCard models have received significant updates to their docstrings, including new examples and best practices. These enhancements clarify how agents should expose their interfaces and how clients should interpret and utilize the transport, url, additional_interfaces, and preferred_transport fields.

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[gemini-code-assist]

Code Review

This pull request updates the A2A type definitions, incorporating pydantic.AnyUrl for URL validation and improving documentation. I suggest using the TransportProtocol enum to enhance type safety and consistency across the models.

[gemini-code-assist]

Consider using the TransportProtocol enum for the transport field instead of str to improve type safety and code clarity. This ensures only valid transport protocols are used, enhancing maintainability.

Suggested change

	transport: str = Field(..., examples=['JSONRPC', 'GRPC', 'HTTP+JSON'])
	transport: TransportProtocol = Field(..., examples=[TransportProtocol.jsonrpc, TransportProtocol.grpc, TransportProtocol.http_json])

[gemini-code-assist]

Leverage the TransportProtocol enum for preferred_transport to improve type safety. Using TransportProtocol.jsonrpc as the default value enhances explicitness and consistency.

Suggested change

	preferred_transport: str | None = Field(
	default='JSONRPC', examples=['JSONRPC', 'GRPC', 'HTTP+JSON']
	)
	preferred_transport: TransportProtocol | None = Field(
	default=TransportProtocol.jsonrpc, examples=[TransportProtocol.jsonrpc, TransportProtocol.grpc, TransportProtocol.http_json]
	)