Perf: avoid parent-wide scans for command insertion

[nguyenyou]

CollectionCommand.Insert currently searches the parent’s children to locate both span boundaries. Walk directly from the start or end sentinel instead, limiting traversal to O(min(abs(index), span size)), independent of unrelated siblings.

Preserve negative indexing and boundary clamping. Count toward zero to handle Int.MinValue without overflow, and report the out-of-range distance and clamped boundary.

Add regression tests for Int.MinValue on populated and empty spans.

Validation: all 10 ChildrenCommandReceiverSpec tests pass under Node.js; git diff --check passes.

[raquo]

Thanks, good efficiency 👍