Allow I/O from larger range of formats

Use optional dependency on external XMP library in order to read from and write to formats not supported by the pure-Python code.

Review the pure-Python format handling and determine how an optional external XMP library would integrate without becoming a required dependency. Identify the formats the library currently cannot read or write, then define completion as successful optional-dependency support for those formats while preserving existing pure-Python behavior.

Written by the indexing model from the issue text.