Invalidate HookRegistry child-registries cache on enable/disable cache (#14093)

* Invalidate HookRegistry child-registries cache on enable/disable cache

* Test the enable-cache-after-inference flow through a pipeline

* Make the FirstBlockCache regression test drive two explicit cache_context forwards

* Drop the pipeline-level enable-cache-after-inference test

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>