docs(q7): document live map pushes and cover them in tests (#927)

The map content trait's module docstring described a pure pull contract --
`refresh()` does I/O, `parse_map_content()` reparses, fields "are then
readable" -- which no longer holds: `update_from_push()` mutates the same
cached fields from the MQTT receive callback and notifies listeners, so
they can change without the reader calling anything. Spell that out.

`docs/DEVICES.md` only mentioned `device.b01_q7_properties` for Q7, so the
push path was undiscoverable and consumers would build a polling loop for
something the device streams by itself. Name the listener entry point and
the fields to read.

The push test checked `image_content` and `raw_api_response` but not
`map_data`, the field carrying the live pose and cleaning path -- dropping
its assignment kept the test green. It also never asserted that no RPC was
published, which is the whole point of the push path: unlike `refresh()`,
it needs no map id and no round trips.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: ximex

docs/DEVICES.md

@@ -21,6 +21,7 @@ Cloud and Network.
         *   Use `device.b01_q10_properties.vacuum` to access vacuum commands (start, pause, stop, dock, empty dustbin, set clean mode, set fan level).
         *   Use `device.b01_q10_properties.command.send()` for raw DP commands.
     *   **Vacuums (B01 Q7)**: Use `device.b01_q7_properties` for Q7 series devices.
+        *   The device streams full map frames on its own while cleaning, so the rendered map stays current without polling or a heartbeat. Register `device.b01_q7_properties.map_content.add_update_listener(cb)` and read `image_content` / `map_data` when notified.
 
 ## Background: Understanding Device Protocols
 

roborock/devices/traits/b01/q7/map_content.py

@@ -6,6 +6,10 @@
 - fields `image_content`, `map_data`, and `raw_api_response` are then readable
 
 For B01/Q7 devices, the underlying raw map payload is retrieved via `MapTrait`.
+
+Q7 devices additionally stream map frames unprompted while cleaning; those arrive
+through `update_from_push()`, which keeps the same cached fields current and
+notifies registered update listeners.
 """
 
 import asyncio

tests/devices/traits/b01/q7/test_map_content.py

@@ -119,8 +119,11 @@ async def test_q7_map_content_updates_from_push(
         fake_channel.map_push_callback(pushed_payload)
 
     assert q7_api.map_content.image_content == b"pngbytes"
+    assert q7_api.map_content.map_data is dummy_map_data
     assert q7_api.map_content.raw_api_response == pushed_payload
     assert updates == [True]
+    # No RPC was needed to get here.
+    assert fake_channel.published_commands == []
 
     await q7_api.close()
     assert fake_channel.map_push_callback is None