test: align test_get_messages with OnMapTrace handler for xmp9ds

A new test asserts that get_message(name, static) returns the right
handler per device class. With the OnMapTrace handler registered for
mowers (xmp9ds), the expected value flips from None to OnMapTrace.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Beennnn

tests/messages/test_get_messages.py

@@ -7,6 +7,7 @@
 from deebot_client.commands.json.error import GetError
 from deebot_client.messages import get_message
 from deebot_client.messages.json.battery import OnBattery
+from deebot_client.messages.json.map import OnMapTrace
 from deebot_client.messages.json.stats import OnStats
 
 if TYPE_CHECKING:
@@ -24,7 +25,7 @@
         ("yna5xi", "GetCleanLogs", None),
         ("yna5xi", "unknown", None),
         ("2pv572", "unknown", None),
-        ("xmp9ds", "onMapTrace", None),
+        ("xmp9ds", "onMapTrace", OnMapTrace),
         ("xmp9ds", "onMapSet", None),
         ("xmp9ds", "onMinorMap", None),
         ("xmp9ds", "onBattery", OnBattery),