Fix Sync ClusterPubSub.disconnect() — Potential AttributeError

[petyaslavova]

Fix Sync ClusterPubSub.disconnect() — Potential AttributeError

Fixes a potential AttributeError in ClusterPubSub.disconnect() when a node's pubsub instance in node_pubsub_mapping has a None connection.
The fix adds a guard check (if pubsub.connection) before calling disconnect(), consistent with the existing check already present for self.connection.
Unit tests are added to verify that disconnect() handles None connections gracefully and still properly disconnects non-None connections.

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Note

Low Risk
Small defensive change in cleanup logic with narrow behavioral impact; tests cover both None and non-None connection cases.

Overview
Prevents ClusterPubSub.disconnect() from raising an AttributeError by guarding pubsub.connection.disconnect() calls for entries in node_pubsub_mapping when their connection is None.

Adds unit coverage to ensure disconnect() is a no-op for None connections and still calls disconnect() on existing connections for both the main pubsub and per-node pubsubs.

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[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}