MNT: Move the Piecewise function to a separate module

Reasons for solving this issue:

The function.py file is already quite big (more than 3.5k code lines).
We should define each class in a separate file, this makes the lib more readable.
There is absolutely no need to define the Piecewise Function class in the same file as the Functionclass

Steps for accomplishing a solution to this issue:

Create a file named rocketpy\mathutils\piecewise_function.py
Move the class PiecewiseFunction(Function): definition to the new file
Updates the mathutils/__init__.py file to ensure the imports are working
Run the tests (make pytest) and verify everything is working properly
Beware of potential breaking changes. What is the behavior of the following command before and after the changes?

from rocketpy.mathutils.function import PiecewiseFunction

MNT: move piecewise functions to separate file

Squashed commit of the following:

Navigation Menu