support receiving a batch of asset paths

currently the API receives a single origin_path for an asset and fetches it. we should also introduce an API that can receive multiple origin_paths at once, be it a path to a dir, a vector, etc. it's not clear to me if we should pick one way (an iter?) or support multiple ways, of doing this, but in general this logic would not add a ton of complexity/maintenance burden (which is also why it seems ok to leave it up to the user to iterate through assets...)

Start with the existing API that accepts one origin_path and trace its asset-fetching path. Decide which batch input shape to support, such as an iterator, directory path, or vector, then verify that multiple asset paths can be received and fetched without adding unnecessary maintenance burden.

Written by the indexing model from the issue text.