fix: re-export symbols in __init__.py files

[anakin87]

Related Issues

• fixes #9506

Proposed Changes:

• re-export symbols in __init__.py files to make shorter imports work without errors/warning from mypy/Pylance.
  • Shorter import example: from haystack.components.builders import ChatPromptBuilder instead of from haystack.components.builders.chat_prompt_builder import ChatPromptBuilder.
• I implemented the solution suggested in the original issue and in Python typing docs

How did you test it?

• CI
• In a fresh virtual environment, I installed Haystack from the current branch. Pylance/mypy errors/warning related to short imports disappeared.

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: and added ! in case the PR includes breaking changes.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 15679340982

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 31 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.2%) to 90.143%

---

Files with Coverage Reduction	New Missed Lines	%
components/embedders/init.py	1	42.86%
components/retrievers/init.py	1	54.55%
components/extractors/init.py	2	60.0%
components/rankers/init.py	2	46.15%
dataclasses/init.py	12	24.0%
utils/init.py	13	20.69%
<!--	Total:	31

Totals
Change from base Build 15679263320:	-0.2%
Covered Lines:	11541
Relevant Lines:	12803

---

💛 - Coveralls

[sjrl]

@anakin87 looks good! Just a few comments.