Use stable user interface in terra

[auenoekologie]

The unstable user interface to terras SpatExtent class changed causing the following error in CRAN checks:

Running examples in ‘hydflood-Ex.R’ failed
The error most likely occurred in:

> ### Name: classifyToPNV
> ### Title: Function to reclassify flood durations to potential natural
> ###   vegetation
> ### Aliases: classifyToPNV
> 
> ### ** Examples
> 
> ## No test: 
>   cache <- tempdir()
>   options("hyd1d.datadir" = cache)
>   options("hydflood.datadir" = cache)
>   options(timeout = 200)
>   library(hydflood)
>   
>   # import the raster data and create a raster stack
>   c <- st_crs("EPSG:25833")
>   e <- ext(309000, 310000, 5749000, 5750000)
>   x <- hydSpatRaster(ext = e, crs = c)
Error in getDEM(filename = tempfile(fileext = ".tif"), ext = ext_int,  : 
  no slot of name "ptr" for this object of class "SpatExtent"
Calls: hydSpatRaster -> getDEM
Execution halted```

[auenoekologie]

Robert Hijmans fixed this initially with his pull request #15.