fix(ci): update actions and use codecov

[110CodingP]

Also removed extraneous commands from the justfile.

[codecov-commenter]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

ℹ️ You can also turn on project coverage checks and project coverage reporting on Pull Request comment

Thanks for integrating Codecov - We've got you covered ☂️

[110CodingP]

🤖 Code Review by Antigravity

Thank you for opening this PR! The workflow modernizations and justfile cleanups are a great improvement. Here is a detailed breakdown of the review.

---

🌟 Positives & Enhancements

• Modern Action Setup: Switched from deprecated actions-rs/toolchain and actions-rs/clippy-check to actions-rust-lang/setup-rust-toolchain@v1, which standardizes Rust installation and caching.
• Automated MSRV Detection: Configured actions-rust-lang/msrv to pull MSRV dynamically from Cargo.toml (1.89.0), eliminating redundant rust-version tracking.
• Documentation Verification: Added a dedicated docs_check step (cargo doc --all-features --no-deps) with warning enforcement (RUSTDOCFLAGS='-D warnings').
• Codecov Integration: Updated coverage reporting to use cargo-llvm-cov with codecov/codecov-action.
• Justfile Refactoring: Removed redundant recipe commands in build, doc, and code_cov.

---

⚠️ Critical Findings & Issues

1. Non-Existent Action Major Versions (actions/checkout@v6, actions/upload-artifact@v7)

• In .github/workflows/code_coverage.yml and .github/workflows/cont_integration.yml, the workflow references actions/checkout@v6 and actions/upload-artifact@v7.
• actions/checkout and actions/upload-artifact are currently at major version v4. Referencing @v6 or @v7 will cause GitHub Actions workflow runs to fail immediately with action resolution errors.
• Recommendation: Revert @v6 and @v7 to @v4 in both workflow files.

2. Duplicate Test Executions in Code Coverage Workflow

• In .github/workflows/code_coverage.yml, cargo llvm-cov is run twice:

  - name: Generate coverage data
    run: cargo llvm-cov --all-features --branch --quiet --lcov --output-path lcov.info
  - name: Generate HTML coverage report
    run: cargo llvm-cov --all-features --branch --quiet --html

• Both commands re-run the full test suite from scratch.
• Recommendation: Combine LCOV and HTML generation into a single step or use cargo llvm-cov report --html for the second step to avoid running tests twice.

3. Slow Source Compilation of cargo-llvm-cov in CI

• In .github/workflows/code_coverage.yml:

  - name: Install cargo-llvm-cov
    run: cargo install cargo-llvm-cov

  cargo install cargo-llvm-cov compiles the binary from source on every CI run (~1–2 minutes overhead).
• Recommendation: Use taiki-e/install-action@cargo-llvm-cov to fetch prebuilt binaries instantly.

4. Least Privilege Workflow Permissions

• In .github/workflows/code_coverage.yml, pull-requests: write permission is granted. Since Codecov upload uses token: ${{ secrets.CODECOV_TOKEN }}, pull-requests: write is unnecessary unless automated PR commenting is explicitly configured. Keeping permissions restricted to contents: read is recommended.

---

💡 Summary Recommendation

Overall, this PR moves CI infrastructure in the right direction! Fixing the action versions (v4 instead of v6/v7) and optimizing the coverage step will make the pipeline fast, reliable, and clean.