Fix: default to status 200 for non-empty DatastarResponse (Litestar) (#39)

Litestar's Stream base class defaults to status 201 when no status_code
is provided. Datastar's client-side fetch action (RC8) only processes
SSE responses with status 200 — non-200 responses are silently discarded:

    // fetch.ts line 561
    if (status !== 200) { dispose(); resolve(); return; }

The empty-content case already defaults to 204. This adds the same
pattern for the non-empty case: default to 200 when the caller doesn't
specify a status code.

Author: tompassarelli

src/datastar_py/litestar.py

@@ -46,6 +46,7 @@ def __init__(
             status_code = status_code or 204
             content = tuple()
         else:
+            status_code = status_code or 200
             headers = {**self.default_headers, **(headers or {})}
         if isinstance(content, DatastarEvent):
             content = (content,)