Fix test_mode propagation by checking dj.config directly

Root cause: When settings.py is first imported, module-level variables like
test_mode are set from sg_config at import time (line 725). Later, when test
fixtures call load_config(test_mode=True), it updates sg_config._test_mode
and dj.config['custom']['test_mode'], but the module-level variable stays stale.

The _test_mode property in BaseMixin was doing:
    from spyglass.settings import test_mode
    return test_mode  # Returns stale module-level variable!

This caused electrode validation to run during tests even though test_mode
should be True, because it was checking the stale module variable that was
set to False at initial import.

Fix: Changed _test_mode to check dj.config['custom']['test_mode'] directly
instead of importing the module-level variable. This avoids global variables
and ensures we always get the current config state.

This is why PR #1454's electrode validation worked on master but failed when
merged with our branch - subtle import order differences meant our branch
triggered settings import earlier, before fixtures could update test_mode.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: edeno

src/spyglass/utils/mixins/base.py

@@ -46,9 +46,11 @@ def _test_mode(self) -> bool:
         - BaseMixin._spyglass_version
         - HelpersMixin
         """
-        from spyglass.settings import test_mode
+        import datajoint as dj
 
-        return test_mode
+        # Check dj.config directly instead of importing module-level variable
+        # which gets stale if load_config() is called after initial import
+        return dj.config.get("custom", {}).get("test_mode", False)
 
     @cached_property
     def _spyglass_version(self):