refactor: converting some DocumentJoiner methods to staticmethod

[davidsbatista]

Proposed Changes:

_concatenate() and _distribution_based_rank_fusion() should be static methods

How did you test it?

• local unit tests
• CI tests

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 12181526861

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.003%) to 90.318%

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Totals
Change from base Build 12163495558:	0.003%
Covered Lines:	8050
Relevant Lines:	8913

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💛 - Coveralls

[Amnah199]

LGTM!

[julian-risch]

LGTM! 👍