lineItemNormalizer.ts: Fix rounding error when normalizing amounts with 7 decimal places

[Kingsman-99]

Description

src/lineItemNormalizer.ts normalizes line-item amounts to 2 decimal places using JavaScript floating-point arithmetic, which introduces rounding errors for values with 7 significant decimal places (Stellar's native precision). The fix should use integer arithmetic in stroops.

Acceptance Criteria

• Amount normalization converts to stroops (integer), rounds, then converts back to decimal string
• normalize(0.0000001) returns '0.00' and normalize(0.0000005) returns '0.00' (document the rounding choice used)
• A regression test covers a value that previously produced an incorrect result
• Unit tests pass

Context

• Target file: src/lineItemNormalizer.ts
• Do not use BigDecimal libraries; use BigInt arithmetic

[yunus-dev-codecrafter]

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

Hi! I've carefully reviewed the entire task description and fully understand the requirements and expected outcome.
I have experience working on similar tasks and I'm confident I can complete this within about an hour. I'd be happy to take ownership of this issue and submit a clean, well-tested solution promptly.
If it's available, please assign it to me. Thank you!

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[supreme2580]

@supreme2580 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer, can I be assigned to this issue?

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[KCEE0901]

@KCEE0901 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hello maintainer , can i work on this

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[drips-wave]

Congratulations, @KCEE0901! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@KCEE0901's PR #721 was approved and merged by @Kingsman-99.

🏆 @KCEE0901: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (319 total points). Track your full progress on GrantFox.

👏 Great work, @KCEE0901! Keep contributing to Stellar-split.

[drips-wave]

This issue has been completed by @KCEE0901 as part of the Stellar Wave Program's 8th Wave 🥳

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