Update Average.java (#5309)

* Update Average.java

- Made the constructor throw an UnsupportedOperationException to prevent instantiation, making it explicit that this is a utility class.
- Added a private validateInput method to handle validation, reducing code duplication and improving readability.
- Consistent exception messages and handling for both methods.
- Improved comments to be more descriptive and follow JavaDoc conventions.
- Enhanced code readability and maintained consistent formatting.

* Minor Update Average.java

* Change To Average.java

* Mnr Average.java

* Update_Average.java

* Fix Average.java

1. throw new IllegalArgumentException("Numbers array cannot be empty or null");

2. int --> double

* fix2.java

return(double)..