[moetemp]

This PR adds the data model of the Streams API in the new temporalio.streams module. That's the StreamRef[T] data, the read items, the errors and the generated wire models that they carry. temporalio.common gets no Stream name.

• A Stream has one payload type, and later calls take it as a type argument. There's no Stream definition.
• StreamRef[T] is data only. It has the fields of the temporal.api.stream.v1.StreamRef wire model (id, owner and backend) and no calls. [Brook S5] Added the client Stream, its typed creates and Stream reads. #375 adds temporalio.client.Stream and [Brook S7] Added Workflow Streams, which write through Local Activities. #377 temporalio.workflow.WorkflowStream, which make the calls.
• A ref converts to the proto JSON of StreamRef through nexgen's generated converter, also as a field of a dataclass or a pydantic model, through the nested conversion of [Brook G2] Converted transfer types nested in JSON values. #368. The type argument, such as StreamRef[Turn], is for type checks only. A ref keeps an owner of any type, and only a close checks it.
• A read item is a Record[T] or a Superseded item. Each has a kind with a Literal type of ItemKind, so a match on r.kind narrows the item's type. There's no close item.
• Superseded.withdrawn_offsets lists only the Records of this read. Superseded.withdraws() answers for any earlier Record, or for just its Producer, with the crate's withdrawal rule on the oneof epoch.
• The module exports the generated wire models that refs, Records and Superseded items carry, such as Producer, ProducerEpoch with its cases, WorkflowTaskEpoch, StreamSuperseded and StreamWriter.
• The errors are written by hand, with the public names, such as StreamAlreadyExistsError, StreamOffsetTooHighError and StreamStorageUnavailableError. Their reason is the proto StreamErrorReason, which the module exports. One helper reads the StreamErrorDetails of a failed call, from a Core error or from the details of an application error, such as a Local Activity or Nexus failure. Only StreamStorageUnavailableError is retryable, and a reason with no class, such as STORAGE_CORRUPT, raises the base StreamError. StreamConfigError isn't a StreamError, since it isn't a Store reason.

Why?

Every later Streams PR builds on these types, and they need no backend or server. Stream handles and big-payload handles discusses the ref's wire form, and why the ref is data with no calls.

Part of the Streams review series.

Checklist

1. How was this tested:
   • tests/contrib/streams/test_refs.py, and test_vectors.py, which checks the vendored Redis proto against the Redis crate, and the Producer ids, the epoch order and the withdrawal rule against the temporalio-streams crate.

[moetemp]

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