Queues: add flow inference to specialized queue compiler

[polybeandip]

Currently, the compiler from PR #2457 ignores class names in the Rio program. Only the position of a node in the tree matters for flow inference: i.e. the compiler would produce the same hardware for

rr[strict[fifo[A], fifo[B]], fifo[C]]

and

rr[strict[fifo[C], fifo[A]], fifo[B]]

It would be nice to remedy this at some point!

Originally posted by @polybeandip in #2460 (comment)