Sessions - refactor and fix bug with file tracking

[lszomoru]

No description provided.

[Copilot]

Pull request overview

Refactors repository-change tracking for Copilot CLI Sessions to avoid stale/incorrect trackers and simplify lifecycle management, addressing a bug in file/change tracking while sessions are active.

Changes:

• Remove per-session Disposable tracking of repository trackers in CopilotCLIChatSessionParticipant, and instead rely on the shared ChatSessionRepositoryTracker to manage tracker lifecycle.
• Update ChatSessionRepositoryTracker.trackRepositoryChanges to be Promise<void> and replace stale trackers when the underlying RepositoryState instance changes.
• Adjust the unit test mock to match the new trackRepositoryChanges return type.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/extension/chatSessions/vscode-node/test/copilotCLIChatSessionParticipant.spec.ts	Updates the repository tracker mock to return void instead of Disposable.None.
src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts	Removes per-session tracker disposal bookkeeping and calls repository tracking without storing a disposable.
src/extension/chatSessions/vscode-node/chatSessionRepositoryTracker.ts	Refactors repository tracking to be internally managed, and adds logic to detect/replace stale trackers based on RepositoryState identity.