fix: parent task not updating when subtask enters FATAL_ERROR state

[Roshan931]

Fixes #492

Root cause

Parent task is never woken when a subtask ends BLOCKED

Changes

• Allow ShouldResumeParentTask to resume a parent when the child task state is BLOCKED, so the engine's wakeParentTask refreshes the parent resolution's next_retry; the parent's subtask step then re-runs, sees the blocked subtask and fails with a client error, blocking the parent task instead of waiting forever. Added a regression test plus two test templates and documented the behaviour in the plugin README.