cleanup and add "trailing_zeroes" argument to si_format()

[machineonamission]

• some random fixes that pycharm wanted me to do
• add strip() calls to si_format(). before, if the prefix was nothing there could be a trailing space
• add trailing_zeroes argument which uses different formatting techniques to include or exclude trailing zeroes (i.e. the 0 in 1.20)

[DrosteEffect]

"before, if the prefix was nothing there could be a trailing space"

That is the correct behavior. A space is always required between the value and the unit, even if no prefix is used: "The numerical value always precedes the unit and a space is always used to separate the
unit from the number".

Source: https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf

For this to be applied consistently, e.g. when directly concatenating the output of si_format() with a unit symbol, the space must be included even when no prefix is used. For example:

"%sV"%si_format(1234)
Out[18]: '1.2 kV'

"%sV"%si_format(123)
Out[19]: '123.0 V'

This is the correct, expected, and consistent behavior.