Stop the slow test packages waiting (closes #263)

- Tests hash passwords at bcrypt.MinCost, set through the
  PasswordCost field of db.Params.
- 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/db/export_test.go

@@ -8,10 +8,12 @@ import (
 	"testing"
 	"time"
 
+	"golang.org/x/crypto/bcrypt"
 	"sneak.berlin/go/neoirc/internal/dbtest"
 )
 
-// NewTestDatabase creates an in-memory database for testing.
+// NewTestDatabase creates an in-memory database for testing. It
+// hashes passwords at bcrypt.MinCost.
 func NewTestDatabase(tb testing.TB) (*Database, error) {
 	tb.Helper()
 
@@ -23,8 +25,9 @@ func NewTestDatabase(tb testing.TB) (*Database, error) {
 	}
 
 	database := &Database{ //nolint:exhaustruct // test helper, params not needed
-		conn: conn,
-		log:  slog.Default(),
+		conn:         conn,
+		log:          slog.Default(),
+		passwordCost: bcrypt.MinCost,
 	}
 
 	err = database.runMigrations(context.Background())