Add plan parent-reduction rule API - #9196

The base and head of this comparison were measured with different runner settings, so their benchmark values are not directly comparable.

What changed between base and head:

• CodSpeed runner v5 changed how benchmarks are measured (base 5.0.1 → head 4.13.0). View release notes
• Cycle estimation (on → off) changes how benchmark performance is calculated. Learn more about cycle estimation

Re-run the base with the same settings to get a valid performance comparison.

_{Comparing vortex-plan-rules (ed09b04) with vortex-plan (bd412f3)}