[FEATURE REQUEST] Add oiiotool `--trim` functionality to ImageBufAlgo

The `--trim` and `--autotrim` arguments to `oiiotool` are very handy for optimizing EXR data windows. That functionality feels like it would be a natural addition to `ImageBufAlgo`, as it would make it easy to use in bespoke processing tools without having to manually replicate the logic from `oiiotool`.

Start by comparing the existing oiiotool --trim and --autotrim behavior with the ImageBufAlgo API and identify the API shape needed for equivalent use in bespoke processing tools. Done means the requested trimming functionality is exposed through ImageBufAlgo with behavior matching the relevant oiiotool operations.

Written by the indexing model from the issue text.