feat(swap): add cancel/expiry sweep worker for stale swap offers

[cypriannwokolo2-creator]

Summary

swap/service.go has no cancel/expiry sweep — stale offers and escrowed funds are never cleaned up.

Acceptance Criteria

• Expiry timestamps + sweep worker
• Escrow release on expiry/cancel
• Tests

Complexity

High.

[CHASE3020]

@CHASE3020 has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

I would love to work on this issue sir

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[dhareymu]

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

Hi maintainer,

Please, I would love to work on this project to fix the issues for you. I promise to work on it swiftly and create a PR for it in no time.

I look forward to working with you. Thank you.

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[Bigdaddyobamo]

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

Good afternoon, Boss Cocor. Please approve this issue so I can handle it.

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[composure-lad]

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

pls assign to me

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[CodeNinjaStephen]

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

Good day maintainer, I’ll love to assist on this issue

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[AbayomiCoded]

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

Hi! I have deep experience implementing background sweep workers with expiry timestamps and atomic escrow release logic, and I can deliver the complete cancel/expiry sweep worker for stale swap offers with comprehensive tests. Please assign the issue to me.

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