[moetemp]

What was changed

This PR adds the Redis Stream backend (temporalio.contrib.stream.RedisStreamBackend) and the in-memory backend for tests (temporalio.contrib.stream.testing.MemoryStreamBackend).

• A client creates a Stream on either with Client.create_stream, which takes backend= for a backend that isn't the default. The package has no create of its own.
• Both call the temporalio-streams runtime that [Brook B1] Added the streams bridge feature that links the temporalio-streams crate. #370 links. The memory backend has Redis's rules, so tests can swap the Store with no other change.
• The clients of one temporalio.runtime.Runtime share one Redis runtime object and its connections. So a service that makes a client for each tenant opens no more connections.
• A standalone Stream expires one Retention after its last write or its close. safety_ttl applies only to an open Stream bound to a Workflow, which this SDK doesn't create yet.
• CI installs redis-server on Linux and macOS, where the Redis lane fails instead of skipping. Redis has no official Windows build, so the lane skips there.
• The live tests run on both backends, with the strict create, the retry of a create with its request id, and a read that ends when a close wakes it. They start their own redis-server, or use TEMPORAL_STREAMS_REDIS_URL.

Why?

These are the first backends that run. From here on, the tests run live on both Stores.

Open question. ExtensionStreamBackend is a public class in a private module, as the base of both backends. Is that OK?

Part of the Streams review series.

Checklist

1. How was this tested:
   • poe lint and pytest tests/contrib/streams on both backends, with Redis required.

[moetemp]

Closed in favor of #381, the combined branch, which has this change.