perf(core): create hot path for unmounting a tree of context #1514

Job	Run time
Build & Test / Build & Test	1m 16s
Prepare environment	5s
Bench text-update / Bench text-update/text-update	45s
Bench create10k / Bench table-app/create10k	2m 19s
Bench filter-list / Bench filter-list/filter-list	1m 31s
Bench hydrate1k / Bench table-app/hydrate1k	1m 55s
Bench many-updates / Bench many-updates/many-updates	1m 34s
Bench replace1k / Bench table-app/replace1k	2m 44s
Bench todo / Bench todo/todo	1m 12s
Bench 03_update10th1k_x16 / Bench table-app/update10th1k	1m 2s
	14m 23s

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