Cost utils validation

[Kieran-Fishwick-TfN]

Describe Changes

Added validation to the cost.utils cost distribution class

Task Checklist

• [ ] Have unittests been added (testing individual functions and their edge cases)
• [ ] Have integration tests been added (if applicable, to test modules of functionality)
• [ ] Have new dependencies been added?
  • [ ] Have they been added to either requirements.txt or requirements_dev.txt.
  • [ ] Have they been added to pyproject.toml