style: Add type hints and doctest to sorts/exchange_sort.py

[Born-as-Harsha]

This PR is a quality and consistency update for the Exchange Sort implementation (created 4 years ago, issue #4600). The entire function structure was updated to meet current repository standards.

Changes include:

• Adding type hints to the function signature (: list, -> list).
• Including a clear doctest example in the docstring.
• Adding the required if __name__ == '__main__': execution block.

Checklist (MANDATORY FIX)

Please read and check all relevant boxes:

• The title of the PR specifies the algorithm/feature being updated or added.
• I have formatted the code to meet the repository's style guidelines.
• I have added type hints to the function signature.
• I have included a doctest within the function's docstring.
• I have ensured the if __name__ == '__main__': block calls doctest.testmod().
• This PR resolves an open issue (If applicable, link it here: #ISSUE_NUMBER).
• I have included a brief explanation of the algorithm (if adding a new one).