Remove the leading blank line in sac.py to comply with PEP8

[songyuc]

The file examples/baselines/sac/sac.py contains an unnecessary leading blank line before the first import statement, which does not conform to Python code style guidelines.

Steps to Reproduce

1. Open examples/baselines/sac/sac.py
2. Observe the first line of the file

Expected Behavior
The file should start directly with the first import statement from collections import defaultdict without any leading blank lines.

Suggested Fix
Remove the initial blank line to align with PEP8 recommendations:
PEP8 - Module Level Dunder Names states that module-level dunder names should come after any module comments and docstrings, but there's no requirement for leading blank lines before imports.

Additional Context
While this is a minor issue, maintaining a consistent code style improves readability and long-term maintainability. I would be happy to submit a PR to address this.