Use phylopics with igraph

[willgearty]

This adds the ability to use phylopic silhouettes as vertices when plotting with igraph. The user must first activate the functionality using the activate_igraph() function, then they can use vertex.shape = "phylopic". I've included (nearly) all of the parameters from add_phylopic_base().

library(rphylopic)
#> You are using rphylopic v.1.5.0.9000. Please remember to credit PhyloPic contributors (hint: `get_attribution()`) and cite rphylopic in your work (hint: `citation("rphylopic")`).
library(igraph)
activate_igraph()
# create a simple graph
g <- make_ring(10)
# plot the graph with phylopics
plot(g, vertex.shape = "phylopic", vertex.color = rainbow(vcount(g)),
     vertex.name = "Gorilla")
#> Warning: You've used the `name` argument. You may want to use `verbose = TRUE`
#> to get attribution information for the silhouette(s).

^{Created on 2025-07-10 with reprex v2.1.1}

TODO:

• Add docs about igraph parameters
• Add tests

Fixes #115

[willgearty]

@schochastics would you be willing to take a look at this?

[schochastics]

This looks good to me!