[moetemp]

What changed?

This PR adds the client target to Python. --targets workflow,client also writes a client package inside the service's output directory, with its own resource classes and a <Service>ClientExtension per service. A client class inherits the extensions and implements _create_nexus_client. A call returns the result with one await.

• The models are generated once, and the client package imports them from ..models. A resource crosses the targets as data, and each side decodes it as its own class.
• The Workflow package doesn't change. A client resource calls its operations through the client that made it. The client is in the private _operations attribute, which isn't a dataclass field, so the resource still converts as data.
• A @nexus.source field is a call parameter, since the client target has no sources yet. The stream WIT has no source, so this first shows in the stream output with the sources of feat: limit @nexus.api-omit to some targets moetemp/nexgen#84.
• Only Python takes the client target, with --native-api and next to workflow. Language::has_client_target lists the languages that have it, so each new language is one line. nexgen refuses the client target for a service with no endpoint, a method name that two services share, an operation named client (the name of the client package), and a resource method that leaves a sourced field to its source. That last check is in resource_plan.rs, so each language calls the same one.

In the stream sample's Python output, stream_service/client/ appears, with its own Stream and StreamServiceClientExtension. The Workflow Stream stays as it is.

Why?

Brook and native Streams call these operations from clients and Activities, not only from Workflow code. With one WIT file, both packages come from the same definitions and have the same names, so the WIT has no copies.

How did you test it?

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests

test_client_target.py runs the stream sample's client package on a fake Nexus client, checks that a handle built by hand has no client, and decodes a Workflow Stream as a client Stream. Rejection fixtures and a unit test cover the refusals.

[tconley1428]

Either workflow has the named module, or they both do.

[moetemp]

Closed in favour of #344