refactor(client)!: reorganize ClientFactory API

[ishymko]

Replace connect class method with create_from_url instance method

1. connect implies some persistent connection, in fact the only difference with create is I/O during agent card resolution (also optional, as it accepted both URL or agent card itself).
2. Contained logic which was useful for a pre-configured factory instance (like agent card resolution).
3. It's a separate async method and create is kept without I/O.

Added a utility create_client module function

One-line entry point similar to the former connect to simplify migration, but doesn't contain any domain logic and just does dispatching between URL and agent card.

[github-actions]

🧪 Code Coverage (vs 1.0-dev)

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	Base	PR	Delta
src/a2a/client/client_factory.py	89.31%	88.67%	🔴 -0.64%
Total	92.49%	92.48%	🔴 -0.01%

Generated by coverage-comment.yml

[gemini-code-assist]

Code Review

This pull request refactors the client creation logic by replacing the ClientFactory.connect class method with a standalone create_client convenience function and expanding the ClientFactory class with create and create_from_url methods. Corresponding updates were made across the codebase and test suites to adopt these changes. A minor improvement was suggested to optimize the ClientFactory.create method by caching the conversion of supported interfaces to a list, thereby avoiding redundant operations.