[moetemp]

What was changed

This PR adds the top-level API of the temporalio-streams runtime, with every call stubbed.

A bridge builds one StreamRuntime per client. The runtime has one typed method for each call, and dispatch.rs has their byte forms for a bridge. StreamRuntime::call takes a method name and the encoded request, and gives back the encoded response or a StreamError. So a bridge decodes no proto, and the Stream logic stays in this crate. sdk-python's bridge does this in temporalio/bridge/src/streams.rs.

Method of call	Request	Response
CreateStream	CreateStreamRequest	CreateStreamResponse
AppendRecords	AppendRecordsRequest	AppendRecordsResponse
CloseStream	CloseStreamRequest	CloseStreamResponse
ReadRecords	ReadRecordsRequest	ReadRecordsResponse
DescribeStream	DescribeStreamRequest	DescribeStreamResponse

A writer is an object that the bridge holds. Dropping it releases it, so no call names a writer by an id.

Writer call	Request	Response
StreamRuntime::open_writer_bytes	OpenWriterRequest	a StreamWriter
StreamWriter::write_bytes	WriteRecordsRequest	WriteRecordsResponse
StreamWriter::close_bytes	none	CloseWriterResponse

• The five methods of call are the Stream service operations. The writer messages are the runtime's own, in coresdk.streams.
• Every call fails with Reason::Unsupported. A byte call decodes its request first, so a request that doesn't decode fails with Reason::Invalid.
• StreamRuntime::new takes a Store, which is an empty trait here. MemoryStreamRuntime builds a runtime for tests from a MemoryStreamConfig, which this PR adds to streams.proto.

Why?

The review of #1733 asked to see the top-level Core API that uses the messages before anything merges into a branch. The PRs on top of this one fill the stubs, from the Store trait to the writers, and none of them changes a public signature in runtime.rs.

Checklist

1. How was this tested:
   • Unit tests that each byte call decodes its request first, and of the answers to an unknown method and a bad memory config. Also cargo clippy and cargo doc with warnings as errors.