Sub-workflow steps were not getting a PVC because the K8s executor
checked context.definition.shared_volume which is the child definition
(e.g. lint) — not the root (ci) that declares shared_volume. Only
root definitions carry the config; sub-workflow definitions don't.
Fix: WorkflowHost::start_workflow_with_name injects the config as
_wfe_shared_volume in instance.data. SubWorkflowStep propagates the
parent's data to children, so the config reaches every descendant.
The K8s executor reads it from workflow.data when
definition.shared_volume is None.
Adds a regression test that mirrors the real topology: a child
workflow instance with root_workflow_id set, no shared_volume on its
definition, and _wfe_shared_volume in data — must still get the PVC.
Pure formatting pass from `cargo fmt --all`. No logic changes. Separating
this out so the 1.9 release feature commits that follow show only their
intentional edits.
