fix: reset alias node counter on dependencies clear

Fixed bug where combining diagrams created duplicate alias nodes (orange
dots for renamed FKs). The issue was that _node_alias_count wasn't reset
when clear() was called, so each load() created new IDs.

Now Person + Marriage shows 2 alias nodes instead of 4.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/dependencies.py

@@ -137,6 +137,7 @@ def __init__(self, connection=None) -> None:
     def clear(self) -> None:
         """Clear the graph and reset loaded state."""
         self._loaded = False
+        self._node_alias_count = itertools.count()  # reset alias IDs for consistency
         super().clear()
 
     def load(self, force: bool = True) -> None: