[moetemp]

What was changed

This PR adds Stream definitions, handles, Records and the Stream errors to temporalio.common, as the data model of the Streams API.

• A definition subclasses StreamDefinition[T] and has @common.defn. It gives a Stream its name and its one payload type, and each handle class is generic in that type, such as ActivityStream[Turn]. There are no Topics, so separate channels are separate Streams.
• StreamHandle converts to the StreamRef proto JSON through G2's nested conversion, so a Workflow can pass it to an Activity, a child or the next run. A Workflow's Stream has owner, an Execution with type EXECUTION_TYPE_WORKFLOW, the Workflow ID as businessId and the first run id as runId. A client's Stream has no owner. The handle keeps its workflow_id and first_execution_run_id properties.
• Record.producer.kind and Superseded.supersession.producer_kind are the generated StreamProducerKind enum, A1's name. The prototype's class was ProducerKind, with the same int values.
• Each error class maps a case of A1's StreamErrorReason, and StreamError.reason is that enum. A reason with no class of its own, such as SEQUENCE, gives StreamError. StreamOptions has what a create sets, Retention for now.
• The ids and withdrawal rules match the crate's, and the tests check them against the crate's shared vectors.
• temporalio.common imports the Stream names on first use, since the Stream modules import temporalio.client and temporalio.workflow. So import temporalio.common loads no Stream module.

Depends on S2 (#372) and G2 (#368). The base is moe/brook/review/feature-streams (G1, G2, G3, S1, S2 and B1), the fork's copy of upstream feature/streams. No changelog fragment, since S9 has the Streams entry.
Part of the Brook review series.

Why?

Every later Streams PR builds on these types. They need no backend and no server.

Open question. temporalio.common gets its first __all__, which changes from temporalio.common import *. Is that OK?

Checklist

1. How was this tested:
   • poe lint, poe gen-docs and pytest tests/contrib/streams on a build with the streams feature.
   • Fork CI passes, except the arm jobs, since the fork has no arm runners.