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_playlist_add_position.py

@@ -97,7 +97,7 @@ def test_putting_a_removed_video_back_leaves_a_linked_list_clean(db, make_user,
     pl.synced_fingerprint = current_fingerprint(db, pl)
     pl.dirty = False
     db.commit()
-    client.delete(f"/api/playlists/{pl.id}/items/b")
+    assert client.delete(f"/api/playlists/{pl.id}/items/b").status_code == 200
     db.expire_all()
     assert db.get(Playlist, pl.id).dirty is True
     _add(client, pl.id, {"video_id": "b", "position": 1})