Improve Dialing

[jacobheun]

Design notes

We have a couple of warts in our dialing system that may cause issues with the new DHT, especially while testing.

• We should fix the simultaneous dial issue and just eat the extra connections. The fact that two nodes can't dial each other at the same time is making testing painful.
• Corollary: the connection manager should trim duplicate unused connections.
• The dialer should really prefer faster transports like QUIC.
• Connections should backoff based on addresses instead of peerIDs.

Testing mechanics

Unit tests.

Success Criteria

• When reuseport is disabled, two peers dialing each other at the same time should succeed.
• Multiple connections should eventually be trimmed.
• If most of the network supports both QUIC and TCP, most connections should be QUIC.

[aschmahmann]

@jacobheun @Stebalien Are we adding "connections should backoff based on addresses instead of peerIDs" to this list?