material scattering coefficients should return a wave

[arturgower]

There are several functions that return the coefficients of a wave basis as a final result. For example, scattering coefficients from a sphere, or the reflection coefficient from a halfspace. Instead, these functions should return a canonical wave which is the scattered wave. This would questions like: what phase should the reflected wave have? What kind of basis should these coefficients have (may potential have azimuth symmetry).

https://github.com/JuliaWaveScattering/EffectiveWaves.jl/blob/c6ad0251604b742097afebff2e86ca5d439786f0/src/acoustics/effective_wave/regular/material_scattering_coefficients.jl#L3

https://github.com/JuliaWaveScattering/EffectiveWaves.jl/blob/c6ad0251604b742097afebff2e86ca5d439786f0/src/acoustics/effective_wave/planewaves/material_scattering_coefficients.jl#L8