Remove automatically_register_units

[chaoming0625]

This pull request includes several changes to the brainunit package, focusing on version updates, string representation improvements, unit registration, and testing enhancements. The most important changes are summarized below:

Version update:

• Updated the version of the brainunit package from 0.0.3 to 0.0.4 in brainunit/__init__.py.

String representation improvements:

• Enhanced the __repr__ and __str__ methods in brainunit/_base.py to handle cases where scale is 0, improving the readability of unit representations. [1] [2]

Unit registration:

• Removed the line that automatically registers units in brainunit/_unit_common.py and dev/units_template.py to prevent unintended unit registrations. [1] [2]

Class instantiation:

• Modified the with_data method in brainunit/sparse/_csr.py to use self.__class__ for creating new instances, ensuring compatibility with subclasses.

Testing enhancements:

• Added a new test case test_matvec_non_unit in brainunit/sparse/_csr_test.py to verify the correctness of matrix-vector multiplication for non-unit data.