Add contract-level test coverage for storage edge cases and boundary values

[ayshadogo]

Review the current storage access patterns and add tests for edge conditions such as empty values, maximum sizes, and invalid ranges.

Acceptance criteria:

• Boundary and invalid-value tests are included.
• The tests capture regressions around storage logic.
• The changes are aligned with the existing test style in the repository.

[neezzha]

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

Hi Maintainer, I reviewed the task carefully and have a clear roadmap for completing it. I'll submit a clean, tested, and well-structured pull request.

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

[Jumongweb]

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

Hi maintainer, i will like to solve this issue

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

[wenxiaojie1]

@wenxiaojie1 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I reviewed the current contract test layout and storage implementations across campaign, donation, withdrawal, escrow, platform config, and dispute arbiter. I can add focused boundary tests for absent keys, zero and maximum values, duplicate operations, authorization failures, persistent and instance storage behavior, and TTL-sensitive paths while keeping each test deterministic. I will run the affected package tests plus the workspace test and clippy checks before the deadline.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @wenxiaojie1 to this issue.

[Phantomcall]

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

Let me work on this for you
i can guarantee that i can delivery high level / high quality code before the deadline tomorrow

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

[devcarole]

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

Hello, I am interested in resolving this task.

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