Update area.cpp(added csa and tsa of cone)

[SHASHWAT2208]

adding the cone curved and total surface area

Description of Change

Added functions to compute:

• Cone Curved Surface Area
• Cone Total Surface Area

Also added corresponding test cases.

All tests are passing locally.

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added tests and example, test must pass
• Added documentation so that the program is self-explanatory and educational - Doxygen guidelines
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes: