Read the panel SSE body from response.content (task 4cbf2e96)

stream_events iterated the aiohttp/HA ClientResponse itself, which is
not async-iterable, so every panel event stream died with "'async for'
requires an object with __aiter__ method, got HassClientResponse" and
reconnected forever. Iterate response.content (the StreamReader)
instead; parsing, close, and the error/retry contract are unchanged.

The streaming test stub in test_sse_subscription.py made the same
mistake (it implemented __aiter__ on the response), which is why the
suite never caught this; it now exposes .content like the real
response. New test_api_client.py tests use a response without
__aiter__ and byte chunks split across frame boundaries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

custom_components/nestquest/api_client.py

@@ -315,7 +315,10 @@ class NestQuestApiClient:
             event_type: str | None = None
             data_lines: list[str] = []
             buffer = ""
-            async for chunk in response:
+            # The body is ``response.content`` (aiohttp's StreamReader,
+            # yielding bytes); the response object itself — HA's
+            # ``HassClientResponse`` included — is NOT async-iterable.
+            async for chunk in response.content:
                 if isinstance(chunk, (bytes, bytearray)):
                     chunk = chunk.decode("utf-8")
                 buffer += chunk