Added the Redis stream provider over External Workflow Streams.

[moedash]

This PR adds RedisStreams, a stream provider over External Workflow Streams that keeps a workflow's streams in a Redis the customer runs.

What changed?

• The transport gains two things a provider needs: subscribe(start_cursor=) seeds a workflow reader from a cursor, and ExternalStreamSubscription.records() yields each value with its offset. The test fakes now place records the way a provider does, since records() needs an offset on each one.
• temporalio.streams.providers.redis.RedisStreams:
  • One Redis log per topic, shared by the workflow and outside readers.
  • A workflow's publishes are staged with its task and promoted once the completion marker proves the task was accepted.
  • Outside appends wake the reader through wake_transport, with counters that follow the entry id order.
  • A retry is matched by the content hash of its plaintext body.
  • Resets, refused wakes on a closing run, and an aborted stage's entries leaving the log.
  • Outside reads at END and last=.
  • Activity streams, standalone streams and workflow tail starts raise StreamUnsupportedError. Later PRs fill those in.
• The stream_reader docstring now says which provider carries a reader across continue-as-new.
• The conformance suite registers the Redis case under STREAMS_LIVE=redis, a live module covers it against a server and a Redis, and CI gets a Redis service.

Part of AI-198 (epic AI-37).

Why?

A Redis store is the provider customers asked for first. The workflow's writes go through the transport's staged commit, so an outside reader never sees a batch from a task History rejected. Replay reads the ranges the markers recorded.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

poe lint is clean at each commit. The external stream suite passes on the dev server. With a local Redis, the streams suite with STREAMS_LIVE=redis passes against a channel server, once with the linked channel kind on and once with it off, so both wake paths ran.