Dimension subclasses should have more specific docstrings

[maffoo]

I noticed that the docstring for tunits.Time and other dimension subclasses inherit their docstrings from the base class:

In [1]: import tunits

In [2]: tunits.Time?
Init signature: tunits.Time(val, unit=None, validate: 'bool' = True)
Docstring:     
Dimension abstraction.

This abstract class allows the creation of values that belong to a dimension
(e.g. t: Time, x: Length, ...etc). This allows us to use static types to check
code correctness (e.g. time_method(t: Time)).

To add a new dimension, create 3 classes:
    - `class _NewDimension(Dimension):` which implements the abstract methods from
        this class.
    - `class NewDimension(_NewDimension, ValueWithDimension)` which represents scalar
        values and doesn't need to implement any methods.
    - `class AccelerationArray(_Acceleration, ArrayWithDimension)` which represents
        an array of values sharing the same dimension and unit.
Init docstring: ValueWithDimension.__init__(self, val, unit=None, validate: bool = True)
File:           ~/.virtualenvs/pyle/lib/python3.12/site-packages/tunits_core.cpython-312-x86_64-linux-gnu.so
Type:           ABCMeta
Subclasses:     

It would be nice to add more informative docstrings for specific dimension classes.

[NoureldinYosri]

@maffoo this can be a project for a 20%er or a community contributor, right?