Reduce example time

[damianooldoni]

Taken from #309 (comment)

While checking the examples of camtraptor v1.0 I get the following note while checking the package:

❯ checking examples ... [115s] NOTE
Examples with CPU (user + system) or elapsed time > 5s
user system elapsed
map_dep 17.33 2.12 36.46
map_summary 16.51 2.20 35.33
get_n_individuals 7.72 0.31 9.00
get_n_obs 4.77 0.16 5.22

This should be solved if we are going to submit to CRAN in the future.