fix(tree): Fix event buffer leak

[Josmithr]

Updates internal withBufferedEvents to simplify its state management to not leverage event listeners, and to ensure that nodes are not leaked.

[github-actions]

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• Correctness — logic errors, race conditions, lifecycle issues
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• API Compatibility — breaking changes, release tags, type design
• Performance — algorithmic regressions, memory leaks
• Testing — coverage gaps, hollow tests

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[Copilot]

Pull request overview

Fixes a memory leak in treeNodeKernel where every KernelEventBuffer permanently subscribed to a module-level flushEventsEmitter, keeping the buffer (and everything its listeners captured) alive for the lifetime of the module even if its owning TreeNodeKernel was dropped without being explicitly disposed. The fix replaces the global emitter with an activeBuffers Set that buffers only opt-in during an active withBufferedTreeEvents window and is drained when the window ends.

Changes:

• Replace flushEventsEmitter subscription with a module-level activeBuffers: Set<KernelEventBuffer> populated only while buffering is active.
• Snapshot-and-clear activeBuffers in withBufferedTreeEvents finally to safely support reentrant calls, and remove the per-instance flush listener / its disposer in KernelEventBuffer.dispose.
• Expose a test-only TEST_activeBufferCount and add regression tests covering baseline, unbuffered, and nested windows.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
packages/dds/tree/src/simple-tree/core/treeNodeKernel.ts	Switch from global flush emitter to opt-in activeBuffers Set; rework dispose; add test accessor.
packages/dds/tree/src/test/simple-tree/core/treeNodeKernel.spec.ts	Add regression tests asserting no buffer retention after/outside/nested buffering windows.