Add a custom EulerAngles class

[deepanshs]

Include EulerAngles class in mrsimulator

class EulerAngles:
    alpha: float
    beta: float
    gamma: float

Define a method __add__ to add two Euler angle.

e1 = EulerAngles(alpha=0.5, beta=3.14, gamma=1.14)
e2 = EulerAngles(alpha=1.2, beta=1.23, gamma=-2.0)
e3 = e1 + e2