Upgrade to adk-python v2.1.0

[krisztianfekete]

Fixes #156

[Copilot]

Pull request overview

This PR upgrades the project’s ADK dependency to the google-adk v2.x line (specifically v2.1.0) to address issue #156 and unlock newer ADK evaluation configuration options (e.g., rubric/criterion knobs mentioned in the issue).

Changes:

• Bump google-adk[eval] dependency to >=2.1.0,<3 (and refresh the lockfile accordingly).
• Make MCP-related unit tests gracefully skip when the [live] extra (and thus mcp) isn’t installed.
• Add a skip guard for Pydantic AI E2E tests when pydantic_ai isn’t installed, and harden the ADK zero-code example against events lacking content.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
pyproject.toml	Updates the direct dependency constraint for google-adk[eval] to v2.1.0+ (bounded below 3).
uv.lock	Lockfile refresh reflecting the new google-adk version and its updated dependency graph.
tests/test_mcp_server.py	Skips the MCP server tests when mcp isn’t available (i.e., without [live] extras).
tests/integration/test_live_agents.py	Skips Pydantic AI live agent tests when pydantic_ai is not installed.
examples/zero-code-examples/adk/run.py	Adds a defensive check for event.content before reading event.content.parts.

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