Run typing checks on our test files

While working on changes to haystack-experimental (https://github.com/deepset-ai/haystack-experimental/pull/430) I wanted to ensure that the protocol I was developing was working as expected with the respective implementations.

I realized though that we never actually test whether our implementations satisfy our protocols since we don't do any type checks on actual test-like code.

Therefore, I think it would be a good idea if we add type checking to our test code in our repos so we can better catch these issues. This will be quite a bit work to get our tests fully compliant but perhaps we could do it in a piece-meal approach where we only turn on type checking in a small part of tests and grow from there.

Components

• test/components/audio/
• test/components/builders/
• test/components/caching/
• test/components/classifiers/
• test/components/connectors/
• test/components/converters/
• test/components/embedders/
• test/components/evaluators/
• test/components/extractors/
• test/components/fetchers/
• test/components/generators/
• test/components/joiners/
• test/components/preprocessors/
• test/components/query/
• test/components/rankers/
• test/components/readers/
• test/components/retrievers/
• test/components/routers/
• test/components/samplers/
• test/components/tools/
• test/components/validators/
• test/components/websearch/
• test/components/writers/

Document Stores

• test/document_stores/

Agents

• test/components/agents/

Other

• test/core/
• test/dataclasses/
• test/evaluation/
• test/fuzz/
• test/hooks/
• test/human_in_the_loop/
• test/marshal/
• test/skill_stores/
• test/testing/
• test/token_counters/
• test/tools/ (top-level, distinct from test/components/tools/)
• test/tracing/
• test/utils/