ci: add job to check imports

[anakin87]

Related Issues

• fixes Add a workflow to test imports #8504

Proposed Changes:

• add a new check-imports job to the tests workflow: running from hatch default environment (with only basic Haystack dependencies), it tries to import each package

  • if everything is OK, the test passes and prints the number of imported packages
  • if there are errors, it fails and shows the stacktrace of each error encountered

• remove test_imports.py test and its dependencies: it was introduced in test: test for missing dependencies #7278, but it never worked and I could not fix it

How did you test it?

• I tried it in this PR: here, it found some errors (one was intentional to test the job; the other had been there for a while :-)) - I'm also fixing them in this PR

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:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 12085867312

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 90.307%

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Totals
Change from base Build 12068906443:	0.0%
Covered Lines:	8031
Relevant Lines:	8893

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💛 - Coveralls