Updated Area.java

[RishitPrabhu]

Summary of Changes:
Added a Helper Method: validatePositive to avoid redundancy.
Consistent Naming: Renamed methods for clarity (e.g., cubeSurfaceArea instead of surfaceAreaCube).
Corrected Exception Handling: Fixed the error message in cylinderSurfaceArea for height validation.
Consistent Documentation: Ensured that all comments consistently refer to the correct terms.

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