Add tests for multisig admin actions

[Levi-Ojukwu]

Description:

The multisig module has helper functions but no integration tests for the full propose → sign → execute flow.

Why it matters: Multisig is a critical security feature that needs thorough testing.

Acceptance Criteria:

• Test propose, sign, execute flow
• Test threshold enforcement
• Test proposal expiration
• Test duplicate signer rejection
• Test only signers can sign

Relevant Files: contracts/invoice_liquidity/src/tests_multisig_admin.rs

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[MoscowDev]

I'd be happy to take this issue on. I have experience building production-ready applications and collaborating effectively through GitHub workflows, including implementing features, resolving bugs, and submitting well-documented pull requests.

I'll carefully review the existing implementation, identify the root cause, and deliver a robust, maintainable solution that aligns with the project's architecture and coding standards. Before submitting my PR, I'll thoroughly test the changes to ensure reliability and avoid regressions.

My goal is to contribute high-quality, clean, and maintainable code while communicating clearly throughout the process and delivering a dependable solution in a timely manner.

[DeFiVC]

@DeFiVC has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I would love to work on this issue.

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

[cristianooR7]

@cristianooR7 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

hello maintainer, i'd lik to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @cristianooR7 to this issue.

[drips-wave]

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

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[drips-wave]

This issue has been completed by @DeFiVC as part of the Stellar Wave Program's 7th Wave 🥳

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