[Documentation Update]: Add GFG Hard problem "BINARY TREE TO DLL" solution

[vansh-codes]

Is there an existing issue for this?

• [X] I have searched the existing issues

Issue Description

Add solution to gfg problem Binary Tree to DLL (HARD)

Suggested Change

Adding solutions (documentation update)

Rationale

No response

Urgency

High

Acknowledgements

• [X] I have read the Contributing Guidelines
• [X] I'm a GSSOC'24 contributor
• [X] I have starred the repository
• [X] I have read and followed the Contribution Guidelines
• [X] I have followed the code style guidelines of this project
• [X] I have checked for any existing open issues that my pull request may address
• [X] I have ensured that my changes do not break any existing functionality
• [X] Each contributor is allowed to create a maximum of 4 issues per day. This helps us manage and address issues efficiently
• [X] I have read the resources for guidance listed below
• [X] I have not used AI-generated content (e.g., ChatGPT, other AI tools)
• [X] I have not used content from existing sites (e.g., text, images)
• [X] I have followed all security rules and only shared trusted resources

[github-actions[bot]]

Hi @vansh-codes! Thanks for opening this issue. We appreciate your contribution to this open-source project. Your input is valuable and we aim to respond or assign your issue as soon as possible. Thanks again!

[github-actions[bot]]

Hello @vansh-codes! Your issue #3293 has been closed. Thank you for your contribution!