Added RemoveStars and ComplexNumberMultiplication

[SwarritSrivastava]

• 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

What does this PR do?

Adds two new string algorithms:

1. RemoveStars

   • Removes each '*' and its closest non-star character to the left.
   • Example: "abbc**def*g" → "abdeg"

2. ComplexNumberMultiplication

   • Multiplies two complex numbers represented as strings.
   • Example: "1+1i" * "1+1i" → "0+2i"

Checklist

• Added Javadoc comments
• Added JUnit tests
• Code passes Checkstyle, PMD, and SpotBugs
• Verified locally with mvn clean verify

This is my contribution for Hacktoberfest 2025

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.83%. Comparing base (9f985b2) to head (5345a68).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6678      +/-   ##
============================================
+ Coverage     75.80%   75.83%   +0.02%     
- Complexity     5804     5810       +6     
============================================
  Files           705      707       +2     
  Lines         19846    19869      +23     
  Branches       3851     3853       +2     
============================================
+ Hits          15045    15068      +23     
  Misses         4218     4218              
  Partials        583      583              

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