feat(socket.io): leave multiple rooms at once

[chojs23]

The kind of change this PR does introduce

• [ ] a bug fix
• [x] a new feature
• [ ] an update to the documentation
• [ ] a code change that improves performance
• [ ] other

Current behavior

Can only leave single room with Socket.leave() method

New behavior

Server-side sockets can now leave several rooms in a single socket.leave([...]) call. The in-memory adapter (and tests) were updated so Adapter.del() accepts a Set<Room>, keeping server state consistent without per-room calls.

Other information (e.g. related issues)

#5391