Feat/imt subarray antenna

[artistrea]

Done

• Added single column subarray implementation to IMT antenna;
• Added tests for Subarray Parameters;
• Added subarray plot implementation;

Missing:

• Tests for subarray implementation;
• correction factor when using subarray (don't even know what it means);

TODO?:

Maybe could be better to refactor the IMT antenna to separate beamforming from array implementation. If implemented separately, subarray and array implementation would be exactly the same, since their formulas for aggregating gain are the same, with the only difference is that the subarray has a constant electrical tilt instead of using it for beamforming.

Example API:

class BeamformingAntenna():
    self.array = Array(sub_array=Array(electrilcal_theta_downtilt=3, element=Element2101(...)))
    # or
    self.array = Array(element=Element2101(...))

    def add_beam(self, phi, theta):
        # since weight and superposition vector are array implementations
        # should memoize them there if don't want to recalculate
        self.beams_list.append((phi, theta))
    
    def calculate_gains():
        for i, phi, theta in zip(something):
            g[i] = self.array.gain(
                self.transform_coordinates_to_local(phi, theta)
            )