auth: Better than the old fix

[bwateratmsft]

Same as #2110 but a better fix.

This is an easier way to understand what's happened, because it skips the added/reverted #2110:
27e1388...ece2793

[bwateratmsft]

@copilot can you review this?

[Copilot]

Pull Request Overview

This PR refactors the event handling mechanism in VSCodeAzureSubscriptionProvider to improve concurrency safety and prevent infinite event loops. The changes implement a lazy listener pattern and add proper synchronization for account state checking.

• Introduces event emitters for sign-in/sign-out events with lazy listener initialization
• Adds promise-based synchronization to prevent race conditions in accountsRemoved()
• Consolidates duplicate event suppression flags into a single suppressEvents variable

Reviewed Changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
auth/src/VSCodeAzureSubscriptionProvider.ts	Refactored event handling with lazy listener initialization, added concurrency-safe accountsRemoved() method, and consolidated event suppression logic
auth/package.json	Bumped version from 5.1.0 to 5.1.1
auth/package-lock.json	Updated lockfile to reflect new version
auth/CHANGELOG.md	Added release notes for version 5.1.1

Files not reviewed (1)

• auth/package-lock.json: Language not supported

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[Copilot]

@bwateratmsft I've opened a new pull request, #2112, to work on those changes. Once the pull request is ready, I'll request review from you.

[bwateratmsft]

I ended up having to combine the timers/suppression. I can't make it work with two separate debounce timers--there's always some way things go wrong. However, I think it's fine--it's not likely the user is simultaneously signing in and signing out.