gcf 0.1.0

• Initial CRAN release.
• GCF variable generation: gcf_field(), with step functions gcf_psi() (11 spatial-pattern operators over buffer radii), gcf_zx() (buffer-wise neighbourhood quantiles) and gcf_reduce() (functional reduction to the X/P/D candidate variables).
• Variable selection: gcf_select() (random forest impurity importance with spatial-block stability resampling and group voting) and gcf_blocks(). gcf_select() seeds the random number generator only when seed is supplied (seed = 1 reproduces the paper) and restores the caller’s generator state on exit.
• Datasets: sim_grid (paper simulation, 900 grid cells) and bio_grid (south-western Australia plant species richness, 6229 grid cells).
• Vignette: “The GCF workflow: from spatial variables to better predictions”.
• Implements Song (2026) doi:10.1080/13658816.2026.2729719; feature generation and selection reproduce the paper’s reference implementation to machine precision.