np_queue made a NetMsg and a buffer per message, every flush a new keep list, and every message
that came in a NetMessage and a buffer; nr_text a new string per text read. A party plays at
dozens a second, so all of it is kept now: a pool of MTU-sized records for the queue (a peer's two
lists swapped by the flush), the inbox's records in two halves swapped when a message finds the
inbox empty, net_written's one record, a relay hello's and a STUN request's bytes in one scratch
buffer, and the texts read out interned. Tests: 6000 messages with the heap flat (Os.heap_bytes),
and an inbox record that holds still across a drain and comes back two drains on.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
