Add string algorithms: RemoveStars and ComplexNumberMultiply

[SYEDMDSAAD]

Feature Added

Added two string algorithms:

1. RemoveStars
   Removes characters affected by '*' in a string.

Example:
Input: leet**cod*e
Output: lecoe

2. ComplexNumberMultiply
   Multiplies two complex numbers represented as strings.

Example:
Input: 1+1i , 1+1i
Output: 0+2i

Both implementations follow repository coding standards and compile successfully.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.33%. Comparing base (1646eda) to head (c8d3895).

Files with missing lines	Patch %	Lines
...in/java/com/thealgorithms/strings/RemoveStars.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #7275   +/-   ##
=========================================
  Coverage     79.32%   79.33%           
- Complexity     6990     6995    +5     
=========================================
  Files           781      783    +2     
  Lines         22958    22976   +18     
  Branches       4510     4513    +3     
=========================================
+ Hits          18212    18227   +15     
- Misses         4019     4020    +1     
- Partials        727      729    +2     

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[DenizAltunkapan]

@SYEDMDSAAD