test: add comprehensive test coverage for Rust modules

[corybuecker]

• Add extensive unit tests for mathematics module (mean, median functions)
• Add comprehensive test coverage for dispersion module (variance, stdev, percentile)
• Include edge case tests for empty arrays, NaN, infinity, and large datasets
• Add rb-sys-test-helpers dependency for Rust testing infrastructure
• Integrate Rust testing into GitHub Actions CI workflow
• Remove unused build.rs file and update Cargo.toml dependencies

[Copilot]

Pull Request Overview

This PR adds comprehensive test coverage for Rust modules in the ruby_native_statistics gem. It introduces Rust testing infrastructure to the CI workflow and adds extensive unit and integration tests.

• Added Rust testing support to GitHub Actions workflow
• Added comprehensive unit tests for mathematical functions with edge cases
• Cleaned up build configuration by removing unused build.rs file

Reviewed Changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
ext/ruby_native_statistics/src/mathematics.rs	Added 20+ unit tests covering mean/median calculations, edge cases, and integration tests
ext/ruby_native_statistics/src/dispersion.rs	Added comprehensive tests for variance, standard deviation, and percentile calculations
ext/ruby_native_statistics/build.rs	Removed unused build.rs file entirely
ext/ruby_native_statistics/Cargo.toml	Updated dependencies and added test-specific dependencies
.github/workflows/branch-protection.yaml	Added Rust toolchain setup and cargo test command

Comments suppressed due to low confidence (3)

ext/ruby_native_statistics/Cargo.toml:13

• The version "0.1" for rb-sys-env in dev-dependencies conflicts with version "0.2" in build-dependencies. This version downgrade in dev-dependencies may indicate a non-existent or incompatible version.

rb-sys-env = { version = "0.1" }

ext/ruby_native_statistics/src/mathematics.rs:100

• Missing test coverage for calculate_mean with empty array. The test only covers calculate_median with empty arrays, but calculate_mean would panic with division by zero on empty input.

    fn test_calculate_median_empty_array() {

ext/ruby_native_statistics/src/mathematics.rs:167

• The NaN test is incomplete - it only verifies that the function doesn't panic but doesn't test the actual behavior. Consider asserting the specific expected result or behavior when NaN values are present.

        let result = calculate_median(&[1.0, f64::NAN, 3.0]);