Update tpi calcs in landscape covariates to terra

[gcperk]

Landscape covar generation is based on spatial::eco rather than terra. Benchmarking tests show approx double the time required and should be updated to terra package. Initial testing indicated some work needs to be done to adjust the normalization factor :

    tic()
    tp <- spatialEco::tpi(dtm, scale=scale, win=win, normalize=TRUE)
    terra::writeRaster(tp, file.path(outpath, "tpi_se.tif"), overwrite = TRUE)
    toc()
    
    tic()
    sd <- focal(dtm, w = scale, fun = "sd", na.policy = "omit") 
    tpi <- terra::terrain(dtm, v = "TPI", neighbors=8)
    dev <- tpi/sd
    toc()
    terra::writeRaster(dev, file.path(outpath, "tpi_terra.tif"), overwrite = TRUE)

TPI 1) Spatial Eco

TPI 2) Terra

Thanks to Josh Evans (Ecora for suggested code improvements)