fix: address issue with createFromArray described in #242

[franzose]

Issue

#242

Summary

1. Preserve explicit position values on initial insert while keeping existing move/update clamping behavior.
2. Ensure createFromArray() inserts are ordered by explicit positions (stable) to avoid sibling reordering shifts.
3. Add regression tests for explicit positions, position gaps, and implicit positioning.
4. Update examples to document the fixed behavior.