Add blank lines to unify code format

[gaogaotiantian]

Normally we do not do PRs with only black line changes. However, if you are interested in this, you can go more thoroughly.

1. I actually prefer 1 blank line between the license header and the first line of code, so let's do that instead of two.
2. For all the imports, split them into two categories and use one blank line to separate them:
   • External libraries
   • Internal imports
3. Sort the libraries alphabetically in each category.
4. Keep two blank lines between the last line of imports and the first line of real code.

[zyckk4]

Thank you for the detailed reply! I have learned a lot.