Directivity example notebook is broken

[MitchellAcoustics]

Looks like we have an issue with directivity.Directivity.using_spherical() not being passed the right args. This is not caught in the directivity tests.

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[2], [line 2](vscode-notebook-cell:?execution_count=2&line=2)
      [1](vscode-notebook-cell:?execution_count=2&line=1) d = Omni()
----> [2](vscode-notebook-cell:?execution_count=2&line=2) fig = d.plot()

File ~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:157, in Directivity.plot(***failed resolving arguments***)
    [155](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:155) # TODO: filename
    [156](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:156) del filename
--> [157](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:157) return plot(self, include_rotation)

File ~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:257, in plot(d, sphere)
    [252](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:252) theta, phi = np.meshgrid(
    [253](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:253)     np.linspace(0.0, np.pi, 50), np.linspace(0.0, +2.0 * np.pi, 50)
    [254](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:254) )
    [256](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:256) # Directivity strength. Real-valued. Can be positive and negative.
--> [257](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:257) dr = d.using_spherical(theta, phi)
    [259](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:259) if sphere:
    [260](https://file+.vscode-resource.vscode-cdn.net/Users/mitch/Documents/GitHub/acoustic-toolbox/examples/~/Documents/GitHub/acoustic-toolbox/acoustic_toolbox/directivity.py:260)     x, y, z = spherical_to_cartesian(1.0, theta, phi)

TypeError: Directivity.using_spherical() missing 1 required positional argument: 'phi'

[MitchellAcoustics]

0d00c8ae40f93850b5e5d16d99ada1aea0b431b2 will resolve this for now. This changes from using d.plot() method to plot(d), since the function seems fine, it's just the class method that is broken. Directivity.plot() method needs to be re-implemented to match the directivity.plot() function signature.