v1.4.0: generic Stream[T] — typed stream messages, drop (T, *Stream, error)

- Stream[T]: Send(v T) type-safe; message type recovered from the
  instantiated Send signature (reflect has no type-args API)
- method signatures reduced to (error), (T, error), (*Stream[T], error);
  the (T, *Stream, error) first-message form is gone — send it via Send
- return T and stream message T now run checkType at bind time
  (Stream[any] remains the explicit untyped escape hatch)
- generated clients: TS onMessage: (data: T); Go <-chan T
- fix vacuous panic assertions (fmt.Sprint(nil) -> "<nil>") in
  hardening/route test catch helpers

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

route_test.go

@@ -120,7 +120,11 @@ func TestBindRouteErrorAndCellUnaffected(t *testing.T) {
 func TestBindRoutePanics(t *testing.T) {
 	f := New()
 	catch := func(fn func()) (msg string) {
-		defer func() { msg = fmt.Sprint(recover()) }()
+		defer func() {
+			if r := recover(); r != nil {
+				msg = fmt.Sprint(r)
+			}
+		}()
 		fn()
 		return ""
 	}