feat: emit a "session-expiry" event when a session has expired

[976520]

The kind of change this PR does introduce

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

Current behavior

When a session expires and is removed in SessionAwareAdapter, no event is emitted, making it impossible for external consumers to detect when a session has expired.

New behavior

SessionAwareAdapter now emits a "session-expiry" event whenever an expired session is deleted. The event handler receives the sid of the expired session as an argument.

Other information (e.g. related issues)

#5250

[darrachequesne]

Hi! Thanks for the pull request.

Could you please explain your use case for this feature?

[976520]

@darrachequesne

Sure!! When using connection state recovery, there's currently no way to know when a persisted session has expired. This makes it difficult to perform cleanup logic tied to session lifetime

e.g.

• Updating a user's online/presence status when their session can no longer be recovered
• Cleaning up server side resources like cached user data that were kept alive in anticipation of reconnection
• Logging or analytics around session recovery failures

Without this event, the only option is to poll or rely on external timeouts, which are harder to synchronize with the actual expiry logic inside SessionAwareAdapter.