internal/pkg: report dependency graph size

This is an interesting value to know when profiling.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg.go

@@ -1111,6 +1111,7 @@ func (c *Cache) Cure(a Artifact) (
 			}
 			n++
 		}
+		c.msg.Verbosef("visited %d artifacts", n)
 	}
 
 	return c.cure(a)