CI: Add code coverage enforcement (minimum 70%)

[LaGodxy]

Summary

Enforce a minimum code coverage threshold in CI to prevent coverage regression.

Implementation

• Coverage threshold: 70% lines, 65% branches
• CI fails if coverage drops below threshold
• Coverage report uploaded to Codecov
• Coverage badge in README
• Per-file coverage in PR comments

[nafsonig]

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

Hello maintainer, please let me work on this issue as soon as possible

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

[drips-wave]

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

🧑‍💻 @nafsonig: 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.

Warning

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🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

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

😎 @nafsonig: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.