Implement property-based testing for payment split calculations

[Kingsman-99]

Overview

The payment split and release-funds logic is tested with fixed examples only. Add property-based tests that generate random inputs and verify invariants hold regardless of values.

Acceptance Criteria

• Property-based tests using proptest or quickcheck crate
• Properties tested:
  • Sum of all recipient payouts equals the total invoice amount (no rounding loss)
  • No recipient receives more than their percentage entitles them to
  • release_funds is idempotent (calling twice does not double-pay)
  • A fully-funded invoice always has funded_amount >= target_amount
  • Recipient percentages always sum to exactly 100
• 1000 random test cases generated per property
• Shrinking enabled: failing case minimized to the simplest reproducer
• Tests run in CI as part of cargo test
• Any property violation blocks merge

[Adesam007-pr3dator]

@Adesam007-pr3dator has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I would like to work on this issue

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[adepoju2006]

@adepoju2006 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I have experience writing property-based tests for financial smart contract logic using proptest. I'll add generative tests for payment split and release-funds calculations, verifying invariants like correct total distribution, no funds lost, and no overflow hold across randomly generated inputs, catching edge cases fixed examples miss.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @adepoju2006 to this issue.

[otobongdev]

@otobongdev has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainer, I can fix this issue

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[Mayorlay]

@Mayorlay has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

HI Maintainer i have reviewed the work and am ready to work on it immediately please assign to me

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[ndyugwu]

@ndyugwu has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

i would like to work on this

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[Caneryy]

@Caneryy has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, can I work on this issue?

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[drips-wave]

Congratulations, @ndyugwu! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @ndyugwu: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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