feat: Add Rust unit tests to CI pipeline (closes #71)

[ada-cinar]

Closes #71

Summary

Adds Rust unit tests, clippy linting, and code formatting checks to the CI/CD pipeline, ensuring Rust core quality is validated before merge.

Changes

1. Rust Unit Tests

• Add cargo test --all-features step
• Runs 6 existing tests:
  • test_lemma_dict_loading
  • test_lookup_lemma_high_frequency_nouns
  • test_lookup_lemma_high_frequency_verbs
  • test_lookup_lemma_oov_words
  • test_lemma_dict_format_validation
  • test_strip_suffixes_basic

2. Rust Linting (Clippy)

• Add cargo clippy -- -D warnings
• Fail build on any clippy warnings
• Enforces Rust best practices

3. Rust Formatting (rustfmt)

• Add cargo fmt --check
• Ensures consistent code style
• Applied cargo fmt to src/lib.rs (whitespace/import order fixes)

4. CI Execution Order

Local Testing

All checks pass:

$ cargo test --all-features
test result: ok. 6 passed; 0 failed

$ cargo clippy -- -D warnings
Finished `dev` profile [unoptimized + debuginfo]

$ cargo fmt --check
(no output = success)

Benefits

1. ✅ Catch Rust-level bugs early - Lemma dict parsing, normalization logic, suffix stripping
2. ✅ Prevent resource loading regressions - Validates embedded stopwords/lemma dict
3. ✅ Enforce code quality - Clippy warnings catch common issues
4. ✅ Consistent formatting - rustfmt ensures uniform style
5. ✅ Documentation via tests - Tests show expected behavior of core functions

Related Issues

• Issue [Test Coverage] Add Native Rust Unit Tests to src/lib.rs #48: "Add Native Rust Unit Tests to src/lib.rs" - tests exist, now run in CI ✅
• Issue [Enhancement] Add Fuzzing Infrastructure for Rust Core #59: "Add Fuzzing Infrastructure for Rust Core" - can build on this CI foundation
• Issue [Enhancement] Add Security Scanning to CI/CD Pipeline (Dependabot + CodeQL) #45: "Add Security Scanning to CI/CD" - should include Rust code scanning

Checklist

• ✅ Add cargo test step to .github/workflows/tests.yml
• ✅ Add cargo clippy for Rust linting
• ✅ Add cargo fmt --check for Rust formatting
• Update CONTRIBUTING.md to mention Rust tests must pass (future)

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Ready for review! 🚀

[fbkaragoz]

@copilot fix the conflict errors if possible

[Copilot]

@fbkaragoz I've opened a new pull request, #137, to work on those changes. Once the pull request is ready, I'll request review from you.