feat: add transaction lock for blockchain requests

[Vidheendu]

📌 Overview

Implemented a transaction locking mechanism to prevent duplicate blockchain requests while a transaction is already in progress.

Features

• Locks the transaction immediately after the first click.
• Prevents duplicate blockchain submissions.
• Ignores repeated clicks until the transaction completes.
• Automatically unlocks after success or failure.
• Displays a notification when users attempt another transaction while one is already running.

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🛠️ Type of Change

• ⛓️ Smart Contract
• 💻 Frontend
• ⚙️ Backend
• 📄 Documentation
• 🧪 Testing

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🔗 Related Issue

Closes #597

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🧪 Testing & Verification

• Frontend verified locally.
• Production build passed (npm run build).
• Duplicate transaction attempts are prevented while a transaction is in progress.

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📸 Screenshots / Demos

(Add screenshots here.)

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✅ PR Checklist

• My code follows the project's style guidelines.
• My changes generate no new warnings.
• Documentation update not required.

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💬 Additional Notes

Implemented a dedicated transaction lock that guards the blockchain transaction handler and releases the lock after the transaction succeeds or fails, reducing the risk of accidental duplicate submissions.

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