feat(agentgateway): make timeout configurable and increase default timeout value

[prashantrakheja]

Description

Increases the timeout value to 60s as a more reasonable default.

The PR makes timeouts configurable for edge cases.

Also, added changes to unwrap ExceptionGroup from async task groups to surface meaningful error messages
(e.g., "MCP Builder destination request failed" instead of "unhandled errors in a TaskGroup")

Type of Change

Please check the relevant option:

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Code refactoring
• Dependency update

Checklist

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• I have read the Contributing Guidelines
• I have verified that my changes solve the issue
• I have added/updated automated tests to cover my changes
• All tests pass locally
• I have verified that my code follows the Code Guidelines
• I have updated documentation (if applicable)
• I have added type hints for all public APIs
• My code does not contain sensitive information (credentials, tokens, etc.)
• I have followed Conventional Commits for commit messages