Improve CI Pipeline: Add Code Coverage Reporting

[Timi16]

Description

Extend the existing GitHub Actions CI pipeline to measure and report code coverage using cargo-llvm-cov, posting a coverage summary on every pull request.

Requirements

• Install and run cargo-llvm-cov in CI
• Generate coverage report in lcov format
• Upload to Codecov or post summary comment on PR
• Set a minimum coverage threshold of 60% (fail CI below this)
• Add coverage badge to README

Suggested Execution

1. Branch: git checkout -b ci/code-coverage
2. Update .github/workflows/ci.yml
3. Add cargo-llvm-cov step after tests
4. Configure Codecov or GitHub PR comment action
5. Add coverage badge to README
6. Commit: ci: add code coverage reporting with cargo-llvm-cov

Acceptance Criteria

• Coverage measured on every PR
• Summary visible on PR page
• Minimum 60% threshold enforced
• Coverage badge in README
• Coverage report downloadable as artifact

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[Samuel1505]

@Samuel1505 has applied to work on this issue as part of the Stellar Wave Program's 2nd wave.

Kindly assign me this issue, i would like to work on it

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Congratulations, @Samuel1505! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on February 26, 2026.

🧑‍💻 @Samuel1505: 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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