[REQUEST] Box search of range search for

### Is your feature request related to a problem? Please describe.
Since openVDB uses a tree structure, is there any way I can efficiently perform a box search to get all values in a BBox ?

No file, test, or entry point is named. Start by locating OpenVDB's tree traversal and query entry points, then determine how a bounding-box range search would fit the existing API. Done requires a defined and tested way to retrieve all values within a requested BBox efficiently.

Written by the indexing model from the issue text.