fix(lib): netio TCP connections run with TCP_NODELAY (bug-1890)

With Nagle on, the small TLS record that ends a burst -- a packet header,
the last short chunk of an HA snapshot, a reply -- waited for the peer's
delayed ACK, ~40 ms on Linux: seen on 5 of 40 snapshot transfers. Set
TCP_NODELAY on every netio TCP socket, outbound (socket_create) and
accepted (socket_accept).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/lib/meson.build

@@ -221,6 +221,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_netio_bounded_connect.c',
                    'testsuite/test_netio_batch_dispatch_uaf.c',
                    'testsuite/test_netio_err_queue.c',
+                   'testsuite/test_netio_nodelay.c',
                    'testsuite/test_request_send_propagation.c',
                    'testsuite/test_raft.c',
                    'testsuite/test_wal_wire.c',