Loopback sockets now get the same event push external sockets earned in PR
#199: the kernel socket table fires edge-triggered readiness callbacks
(empty->nonempty on recv buffers, datagram queues, and listener pending
queues; emitted outside the state lock), the sidecar routes them into
net_socket stream events (data/accept/dgram) keyed by kernel socket id, the
unix reader thread pushes like the TCP one, and the guest gained wake
latches so a wake landing while a pump is active re-pumps instead of
no-oping. Three guest cadence taxes found en route: the per-chunk
yieldBridgeMacrotask (first event-woken chunk now delivers immediately),
and reply-writes issued inside data handlers being microtask-coalesced
(handler-originated writes flush immediately). Loopback peer-wait backoff
capped at 1ms.

Release rows (vs pre-change): tcp_tiny_writes 4.55->3.0ms, udp_echo_big
1.25->0.67, unix_echo_small 5.74->3.5, unix_echo_big 7.38->5-7,
tcp_echo_small 4.02->3.2-4.8, tcp_concurrent 5.82->3.4-5. KNOWN RESIDUAL:
rows are bimodal run-to-run — a wake/pump race remains (event consumed
mid-pump -> EAGAIN -> 10ms park with no re-fire since the edge already
triggered); documented in the backlog for the next pass. http_loopback_get
carries ~+0.3ms from event overhead (0.89->1.16-1.9). Gate green; kernel
edge-trigger unit tests + isolated service regressions for TCP wake/churn,
unix echo, dgram.