Stop the slow test packages waiting (closes #263)

- Tests hash passwords at bcrypt.MinCost through db.PasswordCost.
- Test IRC servers check the queue only on broker notification;
  one test keeps the 100 ms fallback poll.
- The stop-timeout test shortens the timeout through a test-only
  setter.
- service and handlers tests build config.Config directly instead
  of through config.New, so they run in parallel: service had run
  serially, and handlers started its servers one at a time.
- Repeated race trials run as parallel subtests.
- Fixed sleeps become waits on the broker.
- A new test covers the relay's failed queue read, which only the
  100 ms poll had reached.

Model: opus-5-5

internal/ircserver/integration_test.go

@@ -3,7 +3,6 @@ package ircserver_test
 import (
 	"strings"
 	"testing"
-	"time"
 
 	"sneak.berlin/go/neoirc/internal/config"
 )
@@ -1508,9 +1507,6 @@ func TestIntegrationThirdClientObserver(t *testing.T) {
 	bob.joinAndDrain("#trio")
 	carol.joinAndDrain("#trio")
 
-	// Drain join notifications.
-	time.Sleep(100 * time.Millisecond)
-
 	// alice sends; both bob and carol should receive.
 	alice.send("PRIVMSG #trio :hello trio")