chore: CI and dev environment enhancements

[kyokuping]

Summary

This PR integrates just, nextest, and tarpaulin to provide an enhanced local development environment.

Key Changes

• feature: Add justfile for command automation.
• refactor/optimization: Integrate cargo-nextest for faster feedback in pre-commit.
• test:
  • Integrated cargo-tarpaulin for local coverage analysis.
  • Set up code coverage environment in codecov.yaml.
• build: Expanded rust-toolchain.toml to support aarch64-unknown-linux-gnu for cross-platform development.

Details

• Defined recipes such as just setup, just check-deps, and just coverage to streamline repetitive developer actions.
• Added aarch64-unknown-linux-gnu to rust-toolchain.toml to ensure consistent cross-compilation across different development machines and CI.

Technical Notes

• Added cobertura.xml to .gitignore to keep the repository clean.

Quality Control

• Verified local full-check via just ready.
• Passed all hooks via pre-commit run --all-files.
• Confirmed successful compilation for the aarch64 target.

Related Issues

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Flag	Coverage Δ
rust	90.46% <ø> (+0.84%)	⬆️

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see 1 file with indirect coverage changes

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