Reduce memory usage for receive buffers

[Stebalien]

We don't need to keep around large receive buffers. Instead, we can use msgio's message reader to:

1. Read the message length with a small buffer.
2. Get a larger buffer from the buffer pool to read the rest of the message.
3. Put the larger buffer back into the pool.

See https://github.com/libp2p/go-libp2p-kad-dht/blob/c245d836ab82922314dcbc364b3763d114938aad/dht_net.go#L76-L116 for how we do this in the DHT.

[Winterhuman]

@Stebalien Any update on this? Looks like it's been untouched for a while and is blocking ipfs/kubo#6621 (comment).

[amirylm]

Any update on this? we experienced the same issue ssvlabs/ssv#688

[vyzo]

@MarcoPolo would you like to take a swipe at this?

[Wondertan]

Happy to volunteer unless @MarcoPolo wants to tackle this