Tracker revisions, applyImmutable() and applyImmutableBatches() copy each container on a changed path with
spread (Object.assign() onto a null-prototype object) instead of one Object.defineProperty() per key: same own
data properties, prototype and own __proto__ member, about 25 times faster per container. The copy-count test
counts key listings through a proxy instead of spying on Object.keys.
Adds a tracker GC regression test: 10,000 adopted changes retain only the document, not a context registration
per change. Follow-up to #9265.
The delta tracker planned every structural array change with a walk over all
base elements; inserts and removals that keep the remaining elements in order
now get the same plan from the changed ranges alone. applyImmutable built an
appended array as a copy that the insert then grew, a second copy; an append now
builds it with one concat. Ops, values, immutability and errors are unchanged.
32,000 one-item appends, one commit each: 11.3 s -> 1.4 s
(npm run bench:document-append in packages/durable).
