vertices() should do more checking itself

[maelle]

Rather than current situation: + does this work. See paths() and edges() too.

Current list for vertices

• vertices to check length of attributes vs number of names.
• vertices to add names that are character. See case below

library("igraph")
#> 
#> Attaching package: 'igraph'
#> The following objects are masked from 'package:stats':
#> 
#>     decompose, spectrum
#> The following object is masked from 'package:base':
#> 
#>     union
gg <- graph.empty() + vertices(c(1,2,3,4)) + edges(c("1","2","3","4"))
gg + gg
#> Error in `+.igraph`(g, setdiff(uninames, V(g)$name)): Cannot add unknown type to igraph graph

^{Created on 2024-02-26 with reprex v2.1.0}

[maelle]

I no longer understand this issue. 😭