Improve testing framework

A few improvements to our tests to make them more robust and maintainable:

- [ ] Put each inspection test into a separate module
- [ ] Put a JSON golden file with expected inspections for this file
- [ ] Implement testing to compare inspections from files with golden output
- [ ] Implement golden-generator tool to create/update golden tests automatically

The only challenging part of this plan is to come up with some solution for filtering irrelevant inspections for each module, so we have only relevant test-cases.

Start by reviewing the existing inspection tests and how inspections are currently collected; the issue names no files or entry points. Done means separating inspection tests into modules, adding JSON golden files and comparison, providing a golden-generator tool, and defining how irrelevant inspections are filtered.

Written by the indexing model from the issue text.