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'