`P2PStream`, flush once at end of egress batch

[emhane]

Describe the feature

P2Pstream calls poll_flush for each queued egress message, before calling start_send for the next. Instead, poll_flush should only be called once before the loop and once after the loop. According to docs, poll_ready should be called before each call to start_send. So, this also requires modifying poll_ready, to not call poll_flush

This will increase egress throughput. The Sink implementation on the P2PStream, constraints the Sink implementation on all layers above, like EthStream.

https://github.com/paradigmxyz/reth/blob/72f2f1b850a9454789f3ebb3f6efccaee4125659/crates/net/eth-wire/src/p2pstream.rs#L619-L635

https://github.com/paradigmxyz/reth/blob/72f2f1b850a9454789f3ebb3f6efccaee4125659/crates/net/eth-wire/src/p2pstream.rs#L539-L574

Additional context

No response

[github-actions[bot]]

This issue is stale because it has been open for 21 days with no activity.