Add attestInvoice and getAttestations methods

[Kingsman-99]

Overview

Add attestation management methods to StellarSplitClient wrapping the contract's attest_invoice, revoke_attestation, and get_attestations entry points.

Requirements

• client.attestInvoice(invoiceId, statement: string): Promise
• client.revokeAttestation(invoiceId): Promise
• client.getAttestations(invoiceId): Promise<Attestation[]>
• Attestation { attester, statement, timestamp, revoked } type exported
• statement validated to max 256 chars before submission
• Tests: attest, revoke, get list including revoked, statement too long throws

Acceptance Criteria

• All 3 attestation methods implemented
• Attestation type exported
• 256-char statement validation
• Revoked attestations included in get list with revoked: true
• npm test passes with zero failures
• TypeScript compiles with zero errors
• ESLint passes with zero errors

Definition of Done

All CI checks must pass before the PR is reviewed.

[sulaimonifeoluwa4-blip]

@sulaimonifeoluwa4-blip has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

Hi can I work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @sulaimonifeoluwa4-blip to this issue.

[williamsokperez-arch]

@williamsokperez-arch has applied to work on this issue as part of the Stellar Wave Program's 9th wave.

id like to work on this issue

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

[drips-wave]

Congratulations, @williamsokperez-arch! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on September 30, 2026.

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[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox!

@williamsokperez-arch's PR #893 was approved and merged by @Kingsman-99.

🏆 @williamsokperez-arch: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (637 total points). Track your full progress on GrantFox.

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

[drips-wave]

This issue has been completed by @williamsokperez-arch as part of the Stellar Wave Program's 9th Wave 🥳

😎 @williamsokperez-arch: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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