feat(worker)!: promote to v1.0.0 — add Len() to Provider, bump deps to v1

Add Len() int to Provider interface; returns current queue depth for
observability and test assertions. Bump launcher and logz to v1.0.1.
Go directive bumped to 1.26. API committed as stable.

worker_test.go

@@ -180,6 +180,22 @@ func TestWorker_TaskError(t *testing.T) {
 	c.OnStop() // should not panic
 }
 
+func TestWorker_Len(t *testing.T) {
+	c := New(newLogger(), Config{PoolSize: 1, BufferSize: 10, ShutdownTimeout: time.Second})
+	if err := c.OnInit(); err != nil {
+		t.Fatalf("OnInit: %v", err)
+	}
+	// Before start, workers are not running — queued tasks stay in the channel.
+	blocked := make(chan struct{})
+	c.Dispatch(func(ctx context.Context) error { <-blocked; return nil })
+	c.Dispatch(func(ctx context.Context) error { <-blocked; return nil })
+	if got := c.Len(); got != 2 {
+		t.Errorf("Len() = %d, want 2", got)
+	}
+	close(blocked)
+	_ = c.OnStop()
+}
+
 func TestWorker_Lifecycle(t *testing.T) {
 	c := New(newLogger(), Config{PoolSize: 2, BufferSize: 10, ShutdownTimeout: time.Second})
 	if err := c.OnInit(); err != nil {