Drastic strategy change: previously, grids where needlessly synthesised from SH expansions, then we performed grid-node-wise operations (i.e. removing the topographic effect from the gravity disturbance). This was both inefficient and required some workarounds. Main changes: reduction for the topographic effect is performed in the SH coefficients domain (using the operator overloading provided by pyshtools classes) the only grid synthesis performed is the one from topography reduced field to the relevant grids we avoid truncation (the gentle-cut module is left aside), following the Earth2014 Authors recommendation to not do so general refactor, leaner environment.yml updated documentation (in notebook cells)