fix(channelserver): eliminate test log spam, schema errors, and slow setup

Three fixes for the channelserver test suite:

- Add net.ErrClosed check in acceptClients() so a closed listener
  breaks the loop immediately instead of spinning and logging warnings.
  This is correct production behavior too.

- Remove -c flag from pg_restore that conflicted with CleanTestDB's
  prior DROP, causing "gook DROP CONSTRAINT" errors. Clean the schema
  with DROP SCHEMA CASCADE instead of per-table drops.

- Use sync.Once to apply the test schema once per binary run, then
  TRUNCATE tables for isolation. Reduces ~60 pg_restore + 29-patch
  cycles to a single setup pass.

server/channelserver/sys_channel_server.go

@@ -1,6 +1,7 @@
 package channelserver
 
 import (
+	"errors"
 	"fmt"
 	"net"
 	"sync"
@@ -210,7 +211,7 @@ func (s *Server) acceptClients() {
 			shutdown := s.isShuttingDown
 			s.Unlock()
 
-			if shutdown {
+			if shutdown || errors.Is(err, net.ErrClosed) {
 				break
 			} else {
 				s.logger.Warn("Error accepting client", zap.Error(err))