Refactor startup promise orchestration

[Mahathi-s154]

Summary

• replace the mixed named/unnamed PromiseGroup abstraction with a typed resolveNamedPromises helper
• use native Promise.all for notebook display aggregation and command registration
• add focused tests for the new promise resolver and wait for toolbar button creation after command registration

Testing

• npm test -- --runInBand
• npm run lint

[Copilot]

Pull request overview

This PR refactors startup async orchestration by removing the custom PromiseGroup abstraction and replacing it with a typed resolveNamedPromises helper, while simplifying other aggregation points to use native Promise.all.

Changes:

• Replace PromiseGroup with resolveNamedPromises for resolving keyed async dependencies.
• Use Promise.all directly for notebook display data aggregation and command registrations.
• Add unit tests for resolveNamedPromises and ensure toolbar button creation happens after command registration completes.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/utils/promises.ts	Removes PromiseGroup and adds resolveNamedPromises for typed named-promise resolution.
src/index.ts	Updates startup logic to use resolveNamedPromises / Promise.all, and awaits command registration before creating toolbar buttons.
tests/utils/promises.spec.ts	Adds focused Jest coverage for resolveNamedPromises behavior (resolve/empty/reject).

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