Update indent and doc conf

[chaoming0625]

This pull request includes several changes aimed at improving code readability and maintaining consistency in the brainunit package. The most significant changes involve reformatting code for better readability and removing unnecessary blank lines.

Code readability improvements:

• Reformatted the creation of several unit objects in brainunit/_unit_common.py for better readability by adding spaces around operators and breaking long lines. [1] [2] [3] [4] [5]

Code maintenance:

• Removed unnecessary blank lines in various files to maintain code consistency. [1] [2] [3] [4] [5] [6]