improve connection close management

[jacobheun]

Handling multiple connections to a peer
Switch was previously only tracking 1 connection per peer, however it's possible to have more than 1 connection per peer. This adds the ability to track multiple connections per peer, but will attempt to use a single connection when possible.

Closing base connections #288
Switch was previously not properly closing the base connection. This could result in streams staying open on the receiver side if they allow half open connections. Now when a connection is closing, we abort the base pull stream connection to notify the receiver that we're done.

• Ensure there is a transport before filtering dialables.
• Stat starting and stopping are better tied into the switch start and stop

[vasco-santos]

👍