Fix for InitVar and Make

This MR reverts the partial fix from !109 (merged), and supplants it with a complete fix for the InitVar / Make problem introduced in !106 (merged).

The fix adds:

• Build suite stage for running make (just like I added to base package in this MR)
• Resolves flake problems with current InitVar implementation
• Resolves some unrelated flake8 errors that predate any work related to data/buffers attributes

Notes:

• MyPy currently has an internal bug and mishandles InitVar, as does Flake8. I've added comments to temporarily ignore these (erroneous) errors until MyPy and Flake8 can catch up to the python standard library (dataclasses.InitVar). See MyPy Issue for general discussion, and note that the maintainers' views changed during the thread.
• See standard library guidance on "init-only fields" as a subtype of pseudofields
• See also Python typing specification notes on InitVar