chore: add ANN type annotations to stackit, togetherai, unstructured, valkey, watsonx, weave, weaviate

[julian-risch]

Related Issues

None

Proposed Changes:

• Added "ANN" ruleset (flake8-annotations) to ruff select for stackit, togetherai, unstructured, valkey, watsonx, weave, and weaviate integrations
• Added "ANN401" to ruff ignore (allows Any at dynamic/SDK boundaries) for all 7 integrations
• Added "ANN" to tests/**/* per-file-ignores for all 7 integrations (tests don't need type annotations)
• Added "ANN" to examples/**/* (or example/**/*) per-file-ignores where example scripts existed (togetherai, valkey, watsonx, weave)
• Fixed all ANN violations in source files: added -> None to __init__ methods across stackit, togetherai, unstructured, valkey, watsonx, and weaviate; added return types to __str__, resolve_value, _clean_connection_settings, client, and async_client in weaviate
• Added docstrings for two __init__ methods in integrations/unstructured/src/haystack_integrations/components/converters/unstructured/converter.py
  and integrations/valkey/src/haystack_integrations/components/retrievers/valkey/embedding_retriever.py

How did you test it?

Ran tests locally

Notes for the reviewer

StackitChatGenerator test fails because of ClassVar of SUPPORTED_MODELS. Patch release is in progress in Haystack. I wouldn't block the PR because of that. This PR is the last one in the series of PRs that enforce ruff rules for integrations.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.