Include the conversion factor in a Unit

[chaoming0625]

This pull request includes several updates to the brainunit/_unit_common.py file, primarily focusing on the addition of new units and the standardization of formatting for unit creation. The most important changes include adding new derived units, introducing new units for modular dynamics, and standardizing the formatting of existing unit definitions.

This PR enables us to define the unit like

• Electric voltage (eV) 1 eV = 1.602176565 * 10e-19 Joule

>>> import brainunit as u
>>> 1. * u.eV
1. * electronvolt

Close #63

Additions:

• Added new units for modular dynamics, including eV, Angstrom, AMU, and IMF. [1] [2]
• Added new derived units such as ysteradian2, ysteradian3, zsteradian2, zsteradian3, etc.

Formatting Standardization:

• Standardized the formatting for the creation of several units by removing spaces around the ** operator and adjusting the scale formatting. [1] [2] [3] [4] [5]

Minor Changes:

• Added a blank line for better readability in the __all__ list.
• Added comments and section headers to improve code organization and readability.

[Routhleck]

Should also add x=x.factorless() for ldexp?

[Routhleck]

Should also add x=x.factorless() for divmod, power, float_power, multi_dot, matrix_power, and det.

[Routhleck]

Should also add x=x.factorless() for remove_diag, intersect1d, nan_to_num, interp, histogram, take, where, unique and modf.

[Routhleck]

Should also add x=x.factorless() for digitize, allclose, searchsorted,

[Routhleck]

May need to be compatible with units with factors

[Routhleck]

Why __neg__, __pos__, __abs__ need self.factorless()

[Routhleck]

It seems that some methods like transpose do not require factorless()