fix: re-order routes correctly

[kennedymwavu]

closes #109

1. correctly re-order routes by checking the length of the route path itself, and not the pattern.

2. remove redundant chunks in reorder_routes(), specifically:

   new_routes <- as.list(c(seq_len(nrow(df))))
   for(i in seq_len(nrow(df))) {
     new_routes[[i]] <- private$.routes[[df$order[i]]]
   }

   which is identical to private$.routes[df$order] since [ is vectorized.

3. fix failing test on Request by expecting error when non-existent methods are called.

[JohnCoene]

Awesome, thanks!