Added Removing stars and Complex NumberMultiplication

[Ganesh-PC018]

Description

This PR adds the implementation of Complex Number Multiplication under the com.thealgorithms.strings package.

The algorithm multiplies two complex numbers represented as strings (e.g., "1+1i" × "1+1i") and returns their product as a string.

Formula used:
(a + bi) * (c + di) = (ac - bd) + (ad + bc)i

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Type of change

• New Algorithm
• Bug fix
• Refactor
• Documentation update

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Checklist

• I have read the Contributing Guidelines
• The file is in the correct package (com.thealgorithms.strings)
• Code is well-formatted and follows naming conventions
• Added Javadoc comments for all methods and classes
• Code passes all test cases
• I have manually verified example cases:
  • Input: "1+1i", "1+1i" → Output: "0+2i"
  • Input: "1+-1i", "1+-1i" → Output: "0+-2i"

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Additional context

This implementation uses constant time and space complexity (O(1)), relying purely on arithmetic parsing without using any external libraries.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.68%. Comparing base (9484c7e) to head (a04649a).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/strings/RemovingStars.java	0.00%	10 Missing ⚠️
...lgorithms/strings/ComplexNumberMultiplication.java	0.00%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6675      +/-   ##
============================================
- Coverage     75.75%   75.68%   -0.08%     
  Complexity     5772     5772              
============================================
  Files           703      705       +2     
  Lines         19777    19796      +19     
  Branches       3832     3835       +3     
============================================
  Hits          14982    14982              
- Misses         4215     4234      +19     
  Partials        580      580              

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