tests: Enable perplexity integration tests.

[daavoo]

Fixes https://github.com/mozilla-ai/infrastructure/issues/40

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/any_llm/providers/openai/base.py	65.71% <100.00%> (-8.33%)	⬇️
src/any_llm/providers/perplexity/perplexity.py	100.00% <100.00%> (ø)

... and 28 files with indirect coverage changes

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[daavoo]

Integration tests: https://github.com/mozilla-ai/any-llm/actions/runs/17828987307