docs: fix sliding window compaction snippet

[nightcityblade]

Summary

• import EventsCompactionConfig in the standalone sliding-window example
• close the constructor call so the Python snippet is syntactically valid

Testing

• mkdocs build --strict (229 pages indexed; passed)
• parsed the updated sliding-window snippet with Python's ast module

Fixes google/adk-python#6864

[google-cla]

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