FP: Unused variable findings in PEP 484 .pyi type stub files

[mcdigman]

What was flagged?

• File: src/plotly-stubs/basedatatypes.pyi
• Name:_bracket_re, etc

Why is it a false positive?
Type definitions in PEP 484 .pyi stub files should be treated similarly to how skylos now treats PEP 544 Protocols; exempt from being flagged as unused as long as they are not concrete. This is relevant for the many xxx-stubs repos (like plotly-stubs, where I found this issue) that contain only stub files, and so are not expected to have any concrete implementation.

Skylos version
skylos 4.35.0

Minimal reproduction
Any stub in a file named .pyi, in the example, see e.g.

    █  LOW  dead-code/variable  Unused variable: _bracket_re
      Dead Code  src/plotly-stubs/basedatatypes.pyi:16
      evidence: likely dead — no static references were found [analyzer] · symbol is not exported as public API [analyzer] · no package, framework, test,...
      _bracket_re = ...
      Fix: Remove the unused variable if it is not public API.

[duriantaco]

Fixed in #801, now merged into main.