Keep the Client type-hints test green on Python 3.10

typing.get_type_hints(Client) raises TypeError on CPython 3.10 for any
dataclass using KW_ONLY (a stdlib bug fixed in 3.11), which has nothing to
do with the SDK and turned the test red on the 3.10 CI cells. Probe
Client.__init__ instead: it evaluates the same qualified mcp.server
annotation on every supported version.

Author: maxisbey

tests/client/test_client.py

@@ -406,10 +406,12 @@ def test_client_with_url_initializes_streamable_http_transport():
 
 
 def test_client_annotations_still_evaluate_at_runtime():
-    """SDK-defined: `typing.get_type_hints(Client)` resolves even though the server stack is
-    a typing-only import in the client module; the `server` annotation is qualified through
-    the lazy `mcp.server` namespace, which imports it only when the hints are evaluated."""
-    hints = typing.get_type_hints(Client)
+    """SDK-defined: `typing.get_type_hints` on `Client` resolves even though the server stack
+    is a typing-only import in the client module; the `server` annotation is qualified
+    through the lazy `mcp.server` namespace, which imports it only when the hints are
+    evaluated. Probed via `__init__` because class-level `get_type_hints(Client)` trips a
+    CPython 3.10 bug with `KW_ONLY` dataclasses (fixed in 3.11), unrelated to the SDK."""
+    hints = typing.get_type_hints(Client.__init__)
     server_targets = typing.get_args(hints["server"])
     assert MCPServer in server_targets
     assert str in server_targets