feat: more logging & channel changes (relay/flush batching, disconnect handling)

[alepaez]

Lands the last piece of the code that is already deployed in old-dev (hytale-proxy:519dcd3) onto main.

This is Santio's commit da24bf9 from santio/fix/rate-limit-disconnects, cherry-picked onto main after #1/#4 were squash-merged. Authorship is preserved; the tree is identical to that branch. The branch never had a PR, but the deployed server.jar was built from it.

Verification: building :proxy:build from this branch produces a jar whose ac.eva classes are bytecode-identical (javap diff empty) to the server.jar currently on hytale-proxy master. Without this commit, a rebuild from main would regress the deployed proxy.

What it changes:

• HytaleConnection.relay() / flushStreams(): forwarded packets are written without flushing and flushed on channelReadComplete of the peer, instead of per-packet writeAndFlush
• Backend closing the connection now sends the player a "Lost connection to the server" disconnect instead of a bare close
• disconnect() falls back to closing the channel when the send future is null; close() uses closeApplicationConnection
• Warn/error logs on invalid frame length, missing client certificate, inbound stream init failure

Follow-up: rebuild and commit server.jar in hytale-proxy from the resulting main commit so the shipped binary is traceable.

https://claude.ai/code/session_01XtwsBnpBmDn6HWnHh1kNuL