[Example] Benchmark example code

[waltsims]

Describe the example Include the benchmark examples from transcranial simulations as scripts as well as notebooks.

• [ ] 1
• [ ] 2
• [x] 3
• [x] 4
• [ ] 5
• [ ] 6
• [x] 7
• [x] 8
• [ ] 9

Sources The input data for the benchmarks can be found here.

Additional context

• Some can may take while to run, depending on the level of resolution, but the default can be the lowest resolution.
• It makes sense to use scipy.fft rather than scipy.fftpack in utils.filters.py as it does not upcast to np.complex128 which is leading to significant memory issues.
• Example 1-6, are axisymmetric, whose binaries are not supported.