When SCOPED_INCLUDES experiment is enabled:
- Resolve vars from DAG instead of merged vars
- Apply root Taskfile vars first (inheritance)
- Then apply task's source Taskfile vars from DAG
- Apply IncludeVars passed via includes: section
- Skip IncludedTaskfileVars (contains parent's vars, not source's)
This ensures tasks in included Taskfiles see:
1. Root vars (inheritance from parent)
2. Their own Taskfile's vars
3. Vars passed through includes: section
4. Call vars and task-level vars
