[moetemp]

What changed?

This PR adds typed stream topics and StreamRef.

• StreamTopic[T], topic(name, result_type=None) and DEFAULT_TOPIC ("output"). A name holds at most 256 UTF-8 bytes and no control character, the same rule as Core.
• StreamRef round-trips through the default data converter. Its optional chain_run_id picks which chain of a reused Workflow id it names, and never ends a read at that run.
• kind is a plain str, so a ref from a later release still decodes and then meets the kind check.

Why?

Only Workflow-owned streams are in this release. With a string kind, later owner kinds need no type change (DD-2).

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

tests/contrib/streams/test_topics_refs.py.

[moetemp]

Combined into #240.