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.