Examples take too long on CRAN checks

[alancan]

On cran checks we get the following note:

N checking examples (25.6s) Examples with CPU (user + system) or elapsed time > 5s user system elapsed hffmcRaster 6.44 0.10 6.68 fbpRaster 5.44 0.05 5.55

@alancan is resolving in the cran push and will update in repo once fixed.

This does not occur on all machines cran checks, likely temporary solution is to skip these examples (which isn't ideal) though when we update to terra, it sounds like this has already been resolved.

[alancan]

resolved with \donttest{} on the long running tests. The examples are still available for users