add search 2D matrix solutions for both LeetCode variations

[MohakAgrawal25]

• 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

Pull Request Description

What does this PR do?
Adds implementations for the "Search a 2D Matrix" problem (both variations) commonly found on LeetCode (#74 and #240). These algorithms are added under src/main/java/com/thealgorithms/matrix to provide useful matrix search solutions.

Why is this needed?
The current matrix directory lacks solutions for these frequently asked interview problems. Adding them will help learners and contributors understand efficient ways to search in 2D matrices.

Changes made:

• Implemented Search2DMatrix.java containing methods for both matrix search variations.
• Code follows Java naming conventions and project formatting guidelines.
• Added relevant LeetCode URLs and explanations in comments for educational purposes.

Related Issue:
Fixes #6622

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.25000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.75%. Comparing base (a0b6c52) to head (4b2e5ad).

Files with missing lines	Patch %	Lines
.../java/com/thealgorithms/matrix/Search2DMatrix.java	81.25%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6639      +/-   ##
============================================
+ Coverage     75.74%   75.75%   +0.01%     
- Complexity     5765     5774       +9     
============================================
  Files           701      702       +1     
  Lines         19757    19789      +32     
  Branches       3831     3837       +6     
============================================
+ Hits          14964    14991      +27     
- Misses         4214     4217       +3     
- Partials        579      581       +2     

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