fix: clean and simple hang prevention solution

This commit provides a minimal, focused fix for CI hanging issues by addressing the root causes:

**Key Changes:**

1. **ZMQ Resource Management:**
   - Remove `context.term()` calls that were causing hangs
   - Add `socket.setsockopt(zmq.LINGER, 0)` to prevent blocking on close
   - Keep socket operations simple with default timeouts (no artificial limits)

2. **Process Cleanup:**
   - Add timeout (1s) to final `process.wait()` in embedding server manager
   - Prevent infinite waiting that was causing CI hangs

3. **Resource Cleanup Methods:**
   - Add simple `cleanup()` methods to searchers and API classes
   - Focus on C++ object destruction for DiskANN backend
   - Avoid complex cleanup logic that could introduce new issues

4. **Basic Test Safety:**
   - Simple pytest-timeout configuration (300s)
   - Basic test session cleanup using psutil
   - Minimal conftest.py without complex logic

**Philosophy:**
This solution avoids the complex multi-layered fixes from the previous PR chain.
Instead, it targets the specific root causes:
- ZMQ context termination blocking
- Process wait() without timeout
- C++ resource leaks in backends

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

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

packages/leann-backend-diskann/leann_backend_diskann/diskann_backend.py

@@ -459,3 +459,24 @@ class DiskannSearcher(BaseSearcher):
         string_labels = [[str(int_label) for int_label in batch_labels] for batch_labels in labels]
 
         return {"labels": string_labels, "distances": distances}
+
+    def cleanup(self):
+        """Cleanup DiskANN-specific resources including C++ index."""
+        # Call parent cleanup first
+        super().cleanup()
+
+        # Delete the C++ index to trigger destructors
+        try:
+            if hasattr(self, "_index") and self._index is not None:
+                del self._index
+                self._index = None
+                self._current_zmq_port = None
+        except Exception:
+            pass
+
+        # Force garbage collection to ensure C++ objects are destroyed
+        try:
+            import gc
+            gc.collect()
+        except Exception:
+            pass