test: re-render identity preservation tests for ArrayView + React

[Karavil]

Summary

Adds tests verifying that the immutable applyChange pipeline preserves object identity for unchanged nodes (enabling React.memo) while correctly bubbling new references up for changed descendants.

6 of these tests fail on main. This is intentional. They document a regression introduced by expandNode in the change buffering PR. PR #5605 fixes all failures by removing expandNode. Merge both PRs together.

Test results on main

🔴 Failing: identity broken by expandNode eager materialization

expandNode recursively calls Array.from(skipYields(thunk()), expandNode) on every relationship, creating new objects for every node in the tree on every push. This destroys reference identity for all relationship data, meaning React.memo can never skip re-renders for components receiving rows with relationships.

Test	Failure
flat edit: sibling identity	expandNode allocates new objects for all nodes, not just the edited one
child edit bubbles to parent	Eager expansion breaks the identity chain: parent, children array, and sibling child all get new refs when they shouldn't
child add bubbles to parent	Same: expansion allocates new relationship arrays
child remove bubbles to parent	Same
grandchild edit bubbles 3 levels	Same: entire tree gets new objects regardless of what changed
singular relationship: child edit	Same: .one() relationship child gets new ref from expansion

🟢 Passing: no relationship expansion involved

Test	What it verifies
flat add: existing rows keep reference	No relationships, so expandNode doesn't interfere
flat remove: remaining rows keep reference	Same
multiple pushes before flush	Flat list only
listener fires once per flush	Behavioral, not identity
.data reflects changes immediately	Behavioral

🟢 Passing: React layer (ViewWrapper, not ArrayView)

These use mock views, so they test the ViewWrapper/useSyncExternalStore contract independently of the IVM pipeline.

Test	What it verifies
getSnapshot returns same ref without changes	useSyncExternalStore contract: no spurious re-renders
empty snapshots use sentinel objects	Predefined empty tuples prevent re-renders from new empty arrays
row identity preserved in snapshot	ViewWrapper passes through row references from the view
snapshot never goes empty between updates	No data flash between successive data pushes
stale snapshot preserved after destroy	No empty flash on strict mode remount
legitimate empty transition is visible	Server genuinely returns empty then data: transition is not masked
React.memo: only changed row re-renders (mock)	Parent re-renders, unchanged React.memo child skips

🟢 Passing: end-to-end integration (real IVM to React.memo)

Uses QueryDelegateImpl with the test schema (issue → owner, comments) to build a real Source → Join → ArrayView pipeline, wires it directly to useSyncExternalStore, renders React.memo components, then edits a comment and verifies only the affected issue's component re-renders.

issue1 ─── owner:Alice        edit comment1       issue1' ─── owner:Alice (same ref)
        ├── comment1            ──────────►               ├── comment1' (new ref)
        └── comment2                                      └── comment2 (same ref)
issue2 ─── owner:Bob                               issue2 (same ref, unrelated)
        └── comment3                                     └── comment3 (same ref)

<IssueRow issue={issue1}>  re-renders (descendant changed)
<IssueRow issue={issue2}>  skips (React.memo, same ref)

Test	What it verifies
editing a comment only re-renders the parent issue	Full chain: Source push → ArrayView applyChange → identity preservation → useSyncExternalStore → React.memo skip for unrelated rows

Test plan

• All 30 tests pass on fix/remove-eager-expand-node branch (perf: remove eager expandNode from ArrayView #5605)
• 6 tests correctly fail on main (documenting the regression)
• Existing array-view.test.ts and view-apply-change.test.ts still pass

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