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

[Shewale41]

Hey @DenizAltunkapan @yanglbme @alxkm 👋 can you please review this PR , I have cleared all the checks can you merge my PR.
Thanks.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.19608% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.61%. Comparing base (ac6fef1) to head (ca6be2f).

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    #6995      +/-   ##
============================================
+ Coverage     78.57%   78.61%   +0.03%     
- Complexity     6800     6815      +15     
============================================
  Files           763      764       +1     
  Lines         22529    22580      +51     
  Branches       4431     4441      +10     
============================================
+ Hits          17703    17751      +48     
- Misses         4115     4116       +1     
- Partials        711      713       +2     

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