fix(socket-mode): suppress heartbeat warning during shutdown

[Grmiade]

Problem

When a Socket Mode application shuts down, the client sends a WebSocket close frame but leaves its heartbeat interval active until the peer completes the close handshake. If Slack does not send a pong in the 5-second heartbeat window, the SDK logs A pong wasn't received from the server before the timeout of 5000ms! even though the disconnect was intentional.

Solution

Stop heartbeat monitoring immediately for explicit SocketModeClient.disconnect() calls, while preserving heartbeat detection for unexpected connection failures. The close handshake and disconnected lifecycle event remain unchanged.

Validation

• npm run test:unit --workspace @slack/socket-mode
• npx @biomejs/biome check packages/socket-mode/src/SocketModeClient.ts packages/socket-mode/src/SlackWebSocket.ts packages/socket-mode/src/SlackWebSocket.test.ts

[changeset-bot]

🦋 Changeset detected

Latest commit: 2253dff

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@slack/socket-mode	Patch

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