[FEAT] Add Newton's Law of Gravitation algorithm

[Priyanshu1303d]

This PR adds an implementation of Newton's Law of Universal Gravitation (Gravitation.java) to the physics module.

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• 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 src\main\java\com\thealgorithms\physics\Gravitation.java

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This utility class provides two key, related functions:

1. calculateGravitationalForce: Calculates the 2D force vector between two bodies.
2. calculateCircularOrbitVelocity: Calculates the speed required for a stable circular orbit.

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I have run the GravitationTest.java file locally and overall using mvn test, and all tests passed with a BUILD SUCCESS.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.15%. Comparing base (ab65ac6) to head (db04332).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #6855   +/-   ##
=========================================
  Coverage     78.15%   78.15%           
- Complexity     6498     6503    +5     
=========================================
  Files           740      741    +1     
  Lines         21662    21675   +13     
  Branches       4235     4236    +1     
=========================================
+ Hits          16929    16940   +11     
- Misses         4062     4063    +1     
- Partials        671      672    +1     

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