test: Increase test coverage to 95%+ and add coverage reporting

[Haroldwonder]

Audit current test coverage, identify gaps, add missing tests, and integrate coverage reporting into CI.

[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue

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[Ekenesamuel8]

@Ekenesamuel8 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Hello please I will love to work on this task

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[Dami24-hub]

@Dami24-hub has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

i will love to work on this repo

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[drips-wave]

Congratulations, @Dami24-hub! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Dami24-hub: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @Dami24-hub as part of the Stellar Wave Program's 4th Wave 🥳

😎 @Dami24-hub: 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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