feat(invoice): implement invoice expiry indexing for efficient batch_expire

[misrasamuelisiguzor-oss]

Description

The current batch_expire implementation accepts a caller-supplied Vec<u64> of IDs to check. Add an on-chain index of pending invoice IDs so callers can query which IDs are candidates for expiry rather than having to enumerate all IDs externally.

Requirements and context

batch_expire in contracts/invoice/src/lib.rs iterates a caller-provided list. For large invoice volumes this places the enumeration burden on the client. An index stored under a DataKey::PendingIndex key would make off-chain tooling simpler and reduce the chance of missing expired invoices.

Suggested execution

Fork the repo and create a branch:

git checkout -b feature/invoice-pending-index

Implement changes:

• Add DataKey::PendingIndex variant in contracts/invoice/src/invoice.rs
• Update create_invoice to push new IDs onto the index
• Update batch_expire, cancel_invoice, mark_paid, and release_escrow to remove IDs from the index on state change
• Add get_pending_ids read function

Test and commit

Add tests covering add/remove behaviour and verify no regression.

feat(invoice): add pending invoice ID index for efficient batch_expire

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[dextro172-ui]

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[techisigu]

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I am a passionate and results-driven Smart Contract Developer with a proven ability to transform complex business requirements into secure, efficient, and production-ready blockchain solutions. My expertise lies in designing, developing, testing, and deploying decentralized applications and smart contracts that prioritize security, scalability, and performance.

With strong proficiency in both Rust and Solidity, I build robust blockchain systems that are optimized for reliability, gas efficiency, and long-term maintainability. I have hands-on experience developing smart contracts for various decentralized finance (DeFi), tokenization, and Web3 applications, ensuring that every solution adheres to industry best practices and rigorous security standards.

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[samuelisi]

@samuelisi has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I am a passionate and results-driven Smart Contract Developer with a proven ability to transform complex business requirements into secure, efficient, and production-ready blockchain solutions. My expertise lies in designing, developing, testing, and deploying decentralized applications and smart contracts that prioritize security, scalability, and performance.

With strong proficiency in both Rust and Solidity, I build robust blockchain systems that are optimized for reliability, gas efficiency, and long-term maintainability. I have hands-on experience developing smart contracts for various decentralized finance (DeFi), tokenization, and Web3 applications, ensuring that every solution adheres to industry best practices and rigorous security standards.

My experience working with the Stellar SDK enables me to create real-world blockchain applications that facilitate seamless value transfer, financial inclusion, and cross-border transactions. I am skilled in integrating blockchain technologies with modern software architectures, allowing businesses to leverage decentralized systems without compromising usability or performance.

I thrive in collaborative environments, working closely with product teams, designers, and engineers to deliver innovative solutions that solve real-world problems. Whether it's architecting smart contracts, optimizing blockchain infrastructure, conducting security reviews, or building end-to-end decentralized applications, I am committed to delivering high-quality code that is secure, efficient, and built to scale.

My goal is to create blockchain products that not only leverage cutting-edge technology but also provide tangible value to users, businesses, and communities worldwide.

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