Spatial Tessellation, Modeling, and Cross-Validation Toolkit // A modular toolkit for spatial analysis workflows including coordinate reference system management, Voronoi/Delaunay/grid tessellation, feature-to-polygon assignment, geographically weighted regression (GWR, via 'GWmodel'), Bayesian spatial Gaussian process regression (via 'brms'), spatial cross- validation with block and buffered strategies, and model comparison. Provides an S3 class system ('spatial_fit') with consistent predict, fitted, and residuals methods across model backends.