Create Relativity.java

[kvadrik]

Created the file that implements relativity formulae.

• 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 algorithms include a corresponding test class that validates their functionality.
• 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 79.44%. Comparing base (7d57c57) to head (67d40fb).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7323   +/-   ##
=========================================
  Coverage     79.43%   79.44%           
- Complexity     7062     7072   +10     
=========================================
  Files           788      789    +1     
  Lines         23124    23138   +14     
  Branches       4545     4546    +1     
=========================================
+ Hits          18368    18381   +13     
  Misses         4022     4022           
- Partials        734      735    +1     

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