Implement utility functions for list and dict operations

[Emine0010]

Added functions to remove duplicates from a list, count occurrences of elements, and reverse a dictionary.

Describe your changes

Checklist

• [X ] I have read the [CONTRIBUTING]
• [X ] I have performed a self-review of my own code
• [X ] I have run the code locally and it works as expected
• [X ] I have commented my code, particularly in hard-to-understand areas

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