Add missing override keyword to virtual functions in LibUtilities

Issue/feature addressed

Many virtual functions in derived class of the LibUtilities directory do not have the override keyword. This make the code unsafe if someone changes the definition of the base class.

Proposed solution

Add the override keyword to the relevant functions in the LibUtilities directory. The virtual keyword is also explicitly added to all virtual functions.

Tests

Suggested reviewers

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Notes

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Checklist

• [ ] Functions and classes, or changes to them, are documented.
• [ ] User guide/documentation is updated.
• Changelog is updated.
• [ ] Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• [ ] License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).