Input of non-podio-collection types.

The dataservice allows output of stl types and types with dicts, but they actually cannot be read in. Need to update the code in DataHandle::get.

Start in DataHandle::get and compare its input handling with the dataservice paths that already support STL types and types containing dictionaries. Done means non-podio-collection values supported for output can also be read successfully; the issue does not name a specific test, so inspect existing DataHandle tests before running the relevant suite.

Written by the indexing model from the issue text.