Graph tree check

[amankumar100]

Add Graph Tree Check using DFS and Adjacency Matrix

This PR adds a Java implementation to check whether a given undirected graph is a tree. It uses an adjacency matrix as input and applies Depth-First Search (DFS) to:

• Detect cycles
• Ensure the graph is fully connected

Key Points:

• Input: number of nodes and adjacency matrix (1 → edge exists, 0 → no edge)

• No self-loops allowed

• Graph is a tree if:

• No cycles exist

• All nodes are reachable (i.e., graph is connected)

DSA Concept:
This problem falls under Graph Algorithms and uses DFS traversal for verification.

• 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

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 33 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.03%. Comparing base (a8ad162) to head (9b35e09).
⚠️ Report is 409 commits behind head on master.

Files with missing lines	Patch %	Lines
...in/java/com/thealgorithms/tree/GraphTreeCheck.java	0.00%	33 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6318      +/-   ##
============================================
- Coverage     74.17%   74.03%   -0.15%     
  Complexity     5362     5362              
============================================
  Files           678      679       +1     
  Lines         18686    18719      +33     
  Branches       3625     3636      +11     
============================================
- Hits          13860    13858       -2     
- Misses         4272     4306      +34     
- Partials        554      555       +1     

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[siriak]

Please revert changes to configuration files and make sure your code passes checks and there are JUnit tests

[DenizAltunkapan]

@amankumar100 are you still working on it?