add code for isPowerFour

[Vaishnavi5Singh]

• 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 78.06%. Comparing base (48ba1ae) to head (a3718ff).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6916   +/-   ##
=========================================
  Coverage     78.05%   78.06%           
- Complexity     6466     6470    +4     
=========================================
  Files           738      739    +1     
  Lines         21585    21588    +3     
  Branches       4220     4221    +1     
=========================================
+ Hits          16849    16853    +4     
+ Misses         4064     4063    -1     
  Partials        672      672           

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