Bis(η5-cyclopentadienyl)[μ-(4b,5,5a-η3:9b,10,10a-η3)-2,3,7,8-tetrakis(trimethylsilyl)benzo[3,4]cyclobuta[1,2-b]biphenylene]-syn-dicobalt (Co–Co), a Dinuclear π-Complex of the Linear [3]Phenylene Framework