[feat] Add more constants (Unit and Quantity format)

[Routhleck]

This pull request includes several significant changes to the brainunit package, focusing on the removal of unnecessary imports, the addition of new unit constants, and the improvement of unit tests. The most important changes are summarized below:

Removal of Unnecessary Imports:

• brainunit/__init__.py: Commented out the import of constants and its __all__ to reduce redundancy.

Addition of New Unit Constants:

• brainunit/_unit_constants.py: Added multiple new unit constants for mass, angle, pressure, area, volume, speed, temperature, energy, power, and force. [1] [2]

Improvements to Constants:

• brainunit/constants.py: Added new constants for various measurements and removed the __all__ list to streamline the file. [1] [2]

Unit Test Enhancements:

• brainunit/constants_test.py: Introduced a comprehensive list of constants and added a new test to ensure consistency between quantity_constants and unit_constants. [1] [2]

Code Cleanup:

• brainunit/math/_fun_keep_unit.py: Removed the redundant round_ function to clean up the codebase. [1] [2]

[chaoming0625]

Great work.