Add Calculator class with basic operations

[akash-kumar-biswas]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.16%. Comparing base (f57ffa9) to head (cebd3e4).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6535   +/-   ##
=========================================
  Coverage     75.15%   75.16%           
- Complexity     5594     5595    +1     
=========================================
  Files           688      688           
  Lines         19361    19361           
  Branches       3744     3744           
=========================================
+ Hits          14551    14552    +1     
  Misses         4245     4245           
+ Partials        565      564    -1     

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[DenizAltunkapan]

Thank you for your contribution. However, this implementation is not considered an algorithm, and therefore it does not fit the scope of this repository.