Implemented a stop button for BFS/ DFS/ Dijksra visualization

[TejasSaraf]

🛠️ Fixes Issue

Fixes: #496

👨‍💻 Description

-When the "Start BFS" button is clicked, it does not change to "Stop BFS" as expected; both functions are still tied to the same button, but the label remains unchanged. Added a distinct "Stop" button to halt the visualization effectively.

📄 Type of Change

• Bug fix (non-breaking change which fixes an issue)

📷 Screenshots/GIFs (if any)

✅ Checklist

• I am a participant of GSSoC-ext.
• I have followed the contribution guidelines of this project.
• I have viewed deployment of my code.
• My changes generate no new warnings.
• I have made this change from my own.
• I have taken help from some online resources.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have added documentation to explain my changes.

🤝 GSSoC Participation

• This PR is submitted under the GSSoC program.
• I have taken prior approval for this feature/fix.

[github-actions]

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