[moetemp]

What changed?

This PR adds the static calls and the sync call of the Stream runtime. It is the first layer of the thin SDK runtime, which moves Brook's language-neutral runtime out of sdk-python into this crate.

• call_static runs a pure method with no runtime object. DeriveProducer gives the Producer of an Activity attempt from an ActivityContext, which lang copies from its Activity info. ScopedStreamId gives the id of a named Workflow Stream, for code outside a Workflow.
• StreamRuntime::call_sync runs a method that never waits, with no async runtime entered, so a finalizer can call it. call runs those methods too.
• WorkflowTaskAttempt has the field numbers and types of Core's coresdk.activity_task.WorkflowTaskAttempt (C1, fields 1 to 7), so lang passes Core's bytes through. A test encodes Core's message and decodes it as the crate's.
• testdata/producers.json has the Producer of each Activity kind. gen_vectors.py writes it from its second implementation.

Depends on #220 (K10). Review lane is the Rust reviewers.
Part of the Brook review series.

Why?

Brook ships in Python, TypeScript and .NET, so each rule that isn't tied to a language or to Workflow code moves into this crate once. The Producer rule is the first. It reads C1's previous_attempt and previous_started_time too, so the attempt and time tie-break of the withdrawal rule works for every SDK. sdk-python forwards only the started event id today.

How did you test it?

cargo fmt, cargo clippy -- -D warnings (with and without features), cargo test -p temporalio-streams --all-features and cargo doc pass at this commit.

[moetemp]

Parked. Nothing calls these runtime methods yet, since sdk-python does this work in Python. The branch stays, and this layer comes back with its first caller, for example a TypeScript or .NET port or Rust read handles.