Make pyright error on unused variables and imports

[gvanrossum]

• Fixed 23 unused variable errors.
  • This found a bug in answers.py: if N answers present, we'd add N copies of each of the generated answers, due to an unnecessary double loop. What was I thinking?
• Fixed 177 unused import errors.
• Fixed 1 duplicate import error.
• Renamed fixtures.py to conftest.py and remove most imports referencing it from the tests (fixtures defined in conftest.py are implicitly available in all tests).

I used AI (mostly Claude Opus 4.5) for this but reviewed everything it did and occasionally tweaked it (this is how I found the double loop in answers.py).

[gvanrossum]

The 'make format' failures are spurious -- I don't know what causes them (maybe black version skew?) and they don't happen on my Mac. The change looks harmless and not something that should trigger a reformat.

@robgruen this is ready for your review now.

[gvanrossum]

The 'make format' failures are spurious

No they weren't. There was a formatting issue in tools/get_keys.py due to the added warning -- black wants it formatted like this:

        self.credential = (
            DefaultAzureCredential()
        )  # CodeQL [SM05139] - This code is used as part of development setup only.

I'm not sure if CodeQL is smart enough to honor that. Instead we should probably add # fmt: skip to the end of the line, or surround it with # fmt: off / # fmt: on .

@robgruen

[robgruen]

I agree with you about CodeQL I'll make that change.