use outbound only queueing when reentering configuration

[ZECHEESELORD]

Related to #1723

The issue report points at queued play traffic being replayed after the server sends the client back to configuration. On the connected PLAY -> CONFIG path, Velocity was still treating the transition too much like a normal play connection. That left two problems:

• it could queue serverbound play traffic and replay it after the handoff
• it could still forward generic/unknown client packets even when the backend was no longer actually in PLAY

these changes do three things:

• use outbound only queueing for connected PLAY -> CONFIG reconfiguration
• only forward generic/unknown client packets when the backend is open, phase complete, and actually in PLAY
• only forward keepalives when client and backend states match, and only in CONFIG or PLAY

It should be noted that while testing this, I found a second bug on the backend side in Paper where the keepalive tracker survives listener handoff from PLAY to CONFIG, which can leave a stale PLAY expectation alive in the configuration listener under latency.

That fix is separate- with both patches applied, I have not been able to reproduce the full failure anymore.