Bonsai tests: give bSDDClientStub the client baseurl attribute

tool.Bsdd.identifier_url() (pset/ui.py pset name check in the Property
Sets panel) reads client.baseurl unconditionally, but the test stub
never had that attribute, so any scenario that opens the Property Sets
panel dies with AttributeError under the stub. The boolean.feature
scenarios only surfaced this once their STEP id failures were fixed,
the id failure had been masking it. Mirror the real bsdd.Client
default so identifier_url() resolves to the standard identifier URL.

This change was made with the assistance of an AI tool.

src/bonsai/test/bim/stub.py

@@ -21,6 +21,10 @@ from typing import Any, Optional, Union
 
 
 class bSDDClientStub:
+    def __init__(self):
+        # Mirrors bsdd.Client so tool.Bsdd.identifier_url() works against the stub.
+        self.baseurl = "https://api.bsdd.buildingsmart.org/api/"
+
     def get_dictionary(self, dictionary_uri=None, include_test_dictionaries=False):
         dicts = {
             "dictionaries": [