[Ankit-Silwal]

Summary

• Updates Adapter.addSockets, delSockets, and disconnectSockets return types from void to void | Promise<void>
• Updates BroadcastOperator.socketsJoin, socketsLeave, and disconnectSockets to propagate the adapter's return value
• Updates RemoteSocket.join and leave return types accordingly

Context

This is the companion change for socketio/socket.io-redis-adapter#577, which makes the Redis adapter's addSockets/delSockets/disconnectSockets return Promises that resolve once all remote nodes have acknowledged the operation.

Without this change, the Promise returned by the Redis adapter is silently dropped because BroadcastOperator.socketsJoin doesn't return the adapter's result.

Usage

// Before: fire-and-forget, emit may miss remote sockets
io.in(socketId).socketsJoin(room);
io.to(room).emit('event', data);

// After: awaitable, guarantees all nodes have processed the join
await io.in(socketId).socketsJoin(room);
io.to(room).emit('event', data);

Fully backward compatible — the return type is void | Promise<void>, so existing code that doesn't await continues to work unchanged.

Related: #4734

Test plan

• socket.io-adapter TypeScript compilation passes
• Backward compatible — void | Promise<void> is a supertype of both void and Promise<void>
• Integration test with Redis adapter to verify ordering

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