Enable overlap plotting from Python API

[pshriwise]

Description

This adds show_overlaps and overlap_color arguments to the Model.plot method to allow overlap plotting from the Python API.

I've added a test here for a model with an overlap. The image data is interrogated to ensure that the overlap appears correctly.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[paulromano]

Nice addition; thanks!