fix: clear orchestrationQueueSet in InMemoryOrchestrationBackend.reset()

[YunchuWang]

The reset() method clears the orchestrationQueue array but does not clear the orchestrationQueueSet. When an orchestration is created and reset() is called before the orchestration is dequeued, the Set retains the stale instance ID. Any subsequent createInstance() call with the same ID after reset is silently skipped by enqueueOrchestration() because the Set still reports the ID as present.

This causes the orchestration to never be processed.

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[Copilot]

Pull request overview

Fixes a state-reset bug in the in-memory testing backend where reset() cleared the orchestration queue array but left its de-duplication Set populated, preventing re-enqueue of the same instance ID after a reset.

Changes:

• Clear orchestrationQueueSet in InMemoryOrchestrationBackend.reset().
• Add a regression test that reproduces “instance ID reuse after reset” and verifies the orchestration is processed successfully.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/durabletask-js/src/testing/in-memory-backend.ts	Clears the queue de-duplication set during reset() to fully reset queueing state.
packages/durabletask-js/test/in-memory-backend.spec.ts	Adds a regression test ensuring instance IDs can be reused after backend.reset() when an item was still queued.