Add pyright type checking to CI workflow

[conradbzura]

Summary

Add pyright as the project's static type checker and integrate it into the run-tests CI workflow. Fix type errors surfaced by pyright in the loadbalancer, task dispatch, and worker connection modules.

Closes #106

Proposed changes

CI workflow integration

Add a dedicated "Run linter" step to .github/workflows/run-tests.yaml that executes uv run pyright before the test step. This ensures type errors block the pipeline before tests run.

Pyright configuration

Add pyright as a dev dependency and configure [tool.pyright] in wool/pyproject.toml:

• Scope analysis to src/ only
• Exclude __pycache__, build artifacts, tests, and generated protobuf stubs
• Enable reportMissingImports, disable reportMissingTypeStubs

Type fixes — AsyncIterator → AsyncGenerator

RoundRobinLoadBalancer.dispatch and WorkerConnection.dispatch both yield values, making them async generators. Pyright correctly flags the AsyncIterator annotation as incorrect. Replace with AsyncGenerator in both signatures.

Also fix the TYPE_CHECKING import path in roundrobin.py from wool.runtime.work (package) to wool.runtime.work.task (module) to resolve a circular import that pyright surfaces.

Type fixes — WorkTask.dispatch return narrowing

WorkTask.dispatch returns the generic type var W but the _run() and _stream() helpers return concrete types. Wrap both return sites with cast(W, ...) so pyright can verify the generic contract. Add runtime assertions at the top of _run and _stream to guard the callable type assumption.

Test cases

This change is a CI/tooling addition with no new runtime behavior. Type correctness is validated by pyright itself in CI. The existing test suite verifies that the annotation changes introduce no regressions.

Implementation plan

1. • Add pyright to dev dependencies and configure [tool.pyright] in wool/pyproject.toml
2. • Add "Run linter" step to .github/workflows/run-tests.yaml
3. • Fix AsyncIterator → AsyncGenerator in roundrobin.py and connection.py
4. • Fix TYPE_CHECKING import path in roundrobin.py
5. • Add cast() calls and runtime assertions in task.py