super-droplet attribute "alpha" sampling (incl. new example based on Fig 1 from Matsushima et al. 2023) + refactor of the spectral sampling logic to enable deterministic/pseudorandom/quasirandom choice for each sampling type

super-droplet attribute "alpha" sampling (incl. new example based on Fig 1 from Matsushima et al. 2023) + refactor of the spectral sampling logic to enable deterministic/pseudorandom/quasirandom choice for each sampling type #718