Add Support for OASIS Export Format

For as much as I know, DeviceLayout supports 2D layout export primarily to vectorial formats and GDSII. While GDSII is essential for fabrication processes like e-beam lithography, many modern device fabrication flows, increasingly rely on the OASIS format (Open Artwork System Interchange Standard).

Then, it would be highly beneficial to integrate direct support for OASIS export within DeviceLayout.jl, eliminating the need for external conversion tools that could potentially introduce errors or complexity into the workflow.

The issue names DeviceLayout.jl and its existing GDSII and vector export paths, but no files, tests, or entry points. Start by locating the current export implementation and its tests, then compare the required OASIS output with the existing GDSII workflow. Done means DeviceLayout.jl can export layouts directly to OASIS without an external conversion tool.

Written by the indexing model from the issue text.