Event loop is closed when running eval programatically

[sandangel]

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Describe the bug
A clear and concise description of what the bug is.

When extending adk eval and call EvaluationGenerator.generate_responses programatically, it has error "Event loop is closed"

To Reproduce
Steps to reproduce the behavior:

1. Use

asyncio.run(EvaluationGenerator.generate_responses(....))

Expected behavior
A clear and concise description of what you expected to happen.

Should not throw error

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Python version(python -V):
• ADK version(pip show google-adk):

Additional context

I added a PR to fix here: #1408