feat: Implement fixed-point arithmetic module

[cypriannwokolo2-creator]

Description

All financial calculations need fixed-point arithmetic with 7 decimal places (i128) for precision.

Requirements

• Implement math module in common/src/math.rs
• Add fixed-point operations: add, subtract, multiply, divide
• Add overflow protection
• Add tests for edge cases

Acceptance Criteria

• Fixed-point arithmetic maintains precision
• Overflow protection prevents panics
• All financial calculations use fixed-point math
• Tests verify edge cases

Priority

High

[Femaleotaku]

@Femaleotaku has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi, I'd like to work on this issue.

I'll implement this carefully with security as the primary concern, sticking closely to the acceptance criteria and avoiding scope creep.

Planned approach, based on the acceptance criteria:

• Fixed-point arithmetic maintains precision
• Overflow protection prevents panics
• All financial calculations use fixed-point math
• Tests verify edge cases

I'd love the opportunity to work on this — please consider assigning it to me.

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

[acejayl]

@acejayl has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Self contained module with a clear spec, so I can land it cleanly. Plan: common/src/math.rs with i128 fixed point at 7 decimals, add and subtract using checked ops, and multiply and divide going through a widened intermediate before scaling so you don't lose precision or silently wrap halfway through. Every op returns a Result or panics with a typed error rather than overflowing, since a wrong number in financial math is worse than a failed transaction. Tests would cover the edges that actually bite: max and min i128, multiply near the scaling limit, divide by zero, rounding at the 7th decimal, and a few round trips. Happy to take it on.

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

[Ceepr1an]

@Ceepr1an has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I want to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Ceepr1an to this issue.

[drips-wave]

Congratulations, @Femaleotaku! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

🧑‍💻 @Femaleotaku: 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.

Warning

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