flowey: add publish and side_effect shortcuts to PipelineJob

[jstarks]

Building up a pipeline job involves a lot of boilerplate where the caller reaches into dep_on(|ctx| ...) purely to thread a single WriteVar — either from publish_typed_artifact for jobs that produce an artifact, or from new_done_handle for jobs run only for their side effect — into a request. The pattern is so uniform that the closure ends up being a one-liner whose only content is the plumbing itself, which obscures the actual intent of the call site.

This adds two convenience methods on PipelineJob. publish(artifact, f) wraps the publish-typed-artifact pattern, and side_effect(f) wraps the new-done-handle pattern. Both delegate to dep_on under the hood, so there is no new behavior — just a clearer surface for the two most common shapes.

The accompanying sweep through the OpenVMM pipelines (checkin_gates, build_docs, vmm_tests_run) converts every eligible call site to use the new shortcuts. Sites where the closure also threads additional state (e.g. building IGVM, restoring packages) are intentionally left alone: the shortcuts are designed for the single-handle case, and forcing them on mixed-ctx jobs would just reintroduce boilerplate in a different shape. The generated pipeline YAMLs are unchanged.

[Copilot]

Pull request overview

This PR reduces boilerplate in Flowey pipeline definitions by adding two convenience methods to PipelineJob for the two most common dep_on(|ctx| ...) patterns (publishing a typed artifact and running a node purely for side effects), then refactors existing OpenVMM pipelines to use these shortcuts.

Changes:

• Add PipelineJob::publish(artifact, f) as a shortcut for dep_on + ctx.publish_typed_artifact(...).
• Add PipelineJob::side_effect(f) as a shortcut for dep_on + ctx.new_done_handle().
• Update eligible call sites across checkin_gates, build_docs, and vmm_tests_run pipelines to use the new methods.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
flowey/flowey_core/src/pipeline.rs	Adds publish and side_effect convenience methods on PipelineJob that wrap common dep_on plumbing.
flowey/flowey_hvlite/src/pipelines/checkin_gates.rs	Refactors many job steps to use .publish(...) and .side_effect(...) for clearer intent and less boilerplate.
flowey/flowey_hvlite/src/pipelines/build_docs.rs	Replaces dep_on plumbing with .publish(...) / .side_effect(...) in docs pipeline jobs.
flowey/flowey_hvlite/src/pipelines/vmm_tests_run.rs	Converts a side-effect-only job step to use .side_effect(...).