Add workflow-streams sample

[brianstrauch]

Summary

• Ports the five scenarios from samples-python/workflow_streams to TypeScript, using the experimental @temporalio/workflow-streams contrib package on the contrib/pubsub branch of sdk-typescript.
• Scenarios: basic publish/subscribe with heterogeneous topics, reconnecting subscriber, external (non-Activity) publisher, bounded log via truncate(), and LLM token streaming with retry handling.
• Workflow files import from @temporalio/workflow-streams/workflow; client/activity/runner files import from @temporalio/workflow-streams/client. The split keeps the workflow bundle free of crypto/@temporalio/activity/@temporalio/client.
• Depends on the unpublished contrib package via a local `file:` link (`file:../../sdk-typescript/contrib/workflow-streams`). Should switch to a published `^1.17.x` range once the package ships to npm.

Test plan

• `npm install`, `tsc --build`, `eslint .`, `prettier --check .` all clean
• Workflow bundles compile (regression case for the contrib/pubsub split-entrypoints work)
• Scenarios 1–4 run end-to-end against `temporal server start-dev` and produce output shaped like the Python sample
• Scenario 5 verified end-to-end with `OPENAI_API_KEY` set; tokens stream, complete event terminates cleanly
• Retry path for scenario 5 (kill LLM worker mid-stream, confirm ANSI rewind) — not exercised in CI; manual reproduction only

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