Refactor smart contract to use modular library architecture

[Smartdevs17]

Context

Smart contracts need modularization for maintainability.

Current Limitation

Contract logic is monolithic.

Expected Outcome

• Modular contract libraries
• Shared type definitions
• Composable contract architecture
• Improved testability

Acceptance Criteria

• Modular contract libraries
• Shared types crate
• Composable architecture
• No functionality regression
• All existing tests pass
• Gas benchmarks maintained
• Module documentation

Technical Scope

• contracts/subscription/src/ - Subscription contract
• contracts/types/src/ - Shared types
• contracts/ - Contract workspace
• tests/ - Contract tests

[adeboladee]

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

Hello Maintainer, Please I would like to work on this issue

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[ChapmanOfWeb3]

@ChapmanOfWeb3 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello! I’ve reviewed both the requirements and expected behavior. I’m confident I can deliver an implementation that fully meets the project’s expectations.

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[salaudeenkamoldeen99-byte]

@salaudeenkamoldeen99-byte has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello Maintainer! I’ve reviewed the issue and I’m confident I can handle it. I’d appreciate the opportunity to work on it. Please assign it to me if it’s available. Thank you!

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[Itodo-S]

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

Please let me work on this issue; I can handle it

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[Itodo-S]

Fixed in PR #828: #828

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

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