Added threaded binary tree

[Shewale41]

🧩 Add Threaded Binary Tree Implementation

Summary:
This PR adds a Threaded Binary Tree algorithm under com.thealgorithms.datastructures.trees.
It supports efficient in-order traversal without using recursion or a stack by leveraging in-order threading.

Key Features:

• Implements threaded binary tree insertion logic
• Supports in-order traversal via thread links
• Handles duplicate values deterministically (duplicates go to right subtree)
• Includes comprehensive JUnit tests for validation

References:

• Wikipedia: Threaded Binary Tree

Checklist:

• Code follows the repo’s Java and clang-format style
• Added unit tests (ThreadedBinaryTreeTest.java)
• Build and tests pass successfully

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.19608% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.38%. Comparing base (21eff8a) to head (fd840dd).
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
...ithms/datastructures/trees/ThreadedBinaryTree.java	90.19%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6992      +/-   ##
============================================
+ Coverage     78.26%   78.38%   +0.11%     
- Complexity     6573     6631      +58     
============================================
  Files           743      747       +4     
  Lines         21895    22066     +171     
  Branches       4288     4330      +42     
============================================
+ Hits          17137    17296     +159     
- Misses         4074     4080       +6     
- Partials        684      690       +6     

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