fix: Make tests more robust & fix path-handling bugs on macOS

[varungandhi-src]

So it looks like basically there was a bug where the indexer was
generating 0 documents on macOS (related to the recent bug fix in
https://github.com/sourcegraph/scip-python/pull/177/files where we
started normalizing the file paths passed to setTrackedFiles). 😬

However, the tests were passing on macOS not because they were
correct, but because the zero documents case bypassed the
updating/diffing process. 😢

This patch changes the test diffing logic to be more robust, in handling
various scenarios such as 0 documents. It also introduces a couple
of flags, one for filtering tests, and one for running tests with fail-fast
behavior.

On fixing the tests, I discovered some bugs due to improper handling
of case-sensitivity, so I fixed those (which is why the snapshots are unchanged
and the tests are passing on macOS). For some of these, I'm not super
sure about Pyright behavior, so I added a little assertions library
inspired by Antithesis so that we can test the coverage of different
cases by our test suite on macOS.

See also: https://antithesis.com/docs/best_practices/sometimes_assertions/

• Self-review of changes, since Amp did some of the more low-level stuff.

[varungandhi-src]

• chore: Add formatting step in pyright-scip & update CI pipeline #185
• fix: Avoid crash in the presence of decorators. #184
• fix: Make tests more robust & fix path-handling bugs on macOS #183 👈 (View in Graphite)
• scip

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