PING a quiet IRC listener client before closing it (closes #155)

serve closed a connection after five minutes with nothing read and never
sent a PING, so a quiet registered client lost its session. It now sends
PING :<server> after pingInterval with nothing read, and closes the
connection when nothing is read within pongDeadline after that. Every
line read starts both waits again. readTimeout is removed.

Unregistered connections are sent the PING too, so a PONG before
registration is now ignored instead of answered with ERR_NOTREGISTERED.

Model: opus-5-5

internal/ircserver/export_test.go

@@ -13,13 +13,16 @@ import (
 	"sneak.berlin/go/neoirc/internal/service"
 )
 
-// NewTestServer creates a Server suitable for testing.
+// NewTestServer creates a Server suitable for testing, whose
+// connections use interval and deadline in place of
+// pingInterval and pongDeadline.
 // The caller must call Stop() when finished.
 func NewTestServer(
 	log *slog.Logger,
 	cfg *config.Config,
 	database *db.Database,
 	brk *broker.Broker,
+	interval, deadline time.Duration,
 ) *Server {
 	globs := &globals.Globals{
 		Appname:   "neoirc",
@@ -38,6 +41,9 @@ func NewTestServer(
 		brk:      brk,
 		svc:      svc,
 		conns:    make(map[*Conn]struct{}),
+
+		pingInterval: interval,
+		pongDeadline: deadline,
 	}
 }
 
@@ -64,6 +70,14 @@ const KillWriteWindow = killWriteWindow
 // output queue when no broker notification arrives.
 const PollInterval = pollInterval
 
+// PingInterval is how long the server waits with nothing read
+// from a connection before it sends a PING.
+const PingInterval = pingInterval
+
+// PongDeadline is how long the server waits after the PING
+// for a line before it closes the connection.
+const PongDeadline = pongDeadline
+
 // NewTestConn returns a Conn for nick on tcpConn, without a
 // server, database or service behind it.
 func NewTestConn(