Add default client access to convenience API

Exposing `lm.get_default_client()` means that *all* API operations
are available in the convenience API, even if they don't have
dedicated convenience API functions defined.

Author: ncoghlan

src/lmstudio/sync_api.py

@@ -137,6 +137,7 @@
     "LLM",
     "SyncModelHandle",
     "PredictionStream",
+    "get_default_client",
     "embedding_model",
     "list_downloaded_models",
     "list_loaded_models",

tests/test_convenience_api.py

@@ -15,6 +15,12 @@
 )
 
 
+@pytest.mark.lmstudio
+def test_get_default_client() -> None:
+    client = lm.get_default_client()
+    assert isinstance(client, lm.Client)
+
+
 @pytest.mark.lmstudio
 def test_llm_any() -> None:
     model = lm.llm()