Tests for invoice validation

[Atharva0506]

Addressed Issues:

Fixes #148

Screenshots/Recordings:

N/A - This PR strictly introduces automated testing coverage (no UI changes).

Additional Notes:

This PR introduces 100% statement and branch test coverage for the invoice validation and calculation utility functions in the frontend. It resolves edge cases uncovered during testing, such as:

• Properly validating zero/invalid total amounts in batch modes.
• Skipping completely blank line items instead of flagging them as invalid.
• Handling duplicate wallet addresses gracefully in batch invoice configurations.
• Precise percentage-cap validation using BigInt/Wei limits.

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Checklist

• My PR addresses a single issue, fixes a single bug or makes a single improvement.
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• If applicable, I have made corresponding changes or additions to tests
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📥 Commits

Reviewing files that changed from the base of the PR and between 584c0dc and 3994998.

📒 Files selected for processing (4)

• frontend/jest.config.cjs
• frontend/package.json
• frontend/tests/utils/invoiceCalculations.test.js
• frontend/tests/utils/invoiceValidation.test.js

👮 Files not reviewed due to content moderation or server errors (4)

• frontend/tests/utils/invoiceValidation.test.js
• frontend/tests/utils/invoiceCalculations.test.js
• frontend/jest.config.cjs
• frontend/package.json

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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