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/db/auth.go

@@ -14,6 +14,10 @@ var errNoPassword = errors.New(
 	"account has no password set",
 )
 
+// PasswordCost is the bcrypt cost at which SetPassword hashes a
+// password. Tests lower it to bcrypt.MinCost before they start.
+var PasswordCost = bcrypt.DefaultCost //nolint:gochecknoglobals // tests lower it
+
 // SetPassword sets a bcrypt-hashed password on a session,
 // enabling multi-client login via POST /api/v1/login.
 func (database *Database) SetPassword(
@@ -22,7 +26,7 @@ func (database *Database) SetPassword(
 	password string,
 ) error {
 	hash, err := bcrypt.GenerateFromPassword(
-		[]byte(password), bcrypt.DefaultCost,
+		[]byte(password), PasswordCost,
 	)
 	if err != nil {
 		return fmt.Errorf("hash password: %w", err)