test: no test throws a response away; the stream session is narrowed, not baselined

The 7 baselined Optional accesses in plex/stream.py were one fact the type did not carry: the
initial spawn (replace_only=None) always supersedes, so only the fallback respawn can get None.
An assert at the call site says so; the pyright baseline drops 195 -> 188.

test_abuse_limits: the public-URL and YouTube enqueue tests stopped at the profile lookup
(400 no_profile) and passed on that unrelated refusal. They now send an inline spec and assert
the job is queued. The same shape — a request whose response is discarded — sat at 53 more
places across the suite (all returned what they should, measured with a TestClient probe);
each now asserts its status, and test_response_checked keeps it that way (seen red).

backend/tests/test_plex_subtitle_prepare.py

@@ -208,7 +208,7 @@ def test_an_unshowable_track_says_why_and_maps_to_a_status(client, monkeypatch):
         raise subtitles.SubtitleUnavailable("bitmap")
 
     monkeypatch.setattr(subtitles, "_extract_and_publish", _bitmap)
-    client.get("/api/plex/subtitle/98614/0/status")
+    assert client.get("/api/plex/subtitle/98614/0/status").status_code == 200
     pool.run_all()
     st = client.get("/api/plex/subtitle/98614/0/status").json()
     assert st["state"] == "failed" and st["code"] == "bitmap"