test(rust): move large unit tests out of implementation files

[nachiketb-nvidia]

What

Moves the largest inline Rust unit-test modules into sibling *_tests.rs files while keeping each module registered as mod tests through #[path = "..."].

Extracted files:

• crates/libsy/src/algorithms/util/affinity.rs -> affinity_tests.rs
• crates/switchyard-translation/src/helpers.rs -> helpers_tests.rs
• crates/libsy/src/algorithms/stage.rs -> stage_tests.rs
• crates/libsy/src/algorithms/rand.rs -> rand_tests.rs
• crates/libsy/src/core/classifier.rs -> classifier_tests.rs

Why

These were the obvious inline-test-heavy Rust files where test LoC was much larger than implementation LoC. Keeping the tests in sibling files makes the implementation files easier to read without changing test visibility or behavior.

How

Each implementation file now ends with:

#[cfg(test)]
#[path = "<name>_tests.rs"]
mod tests;

Because the external file is still compiled as the same child tests module, the moved tests retain the same super::* access to private implementation details. No test macros or new abstraction layer were added.

Validation

• cargo fmt --all --check
• cargo test -p switchyard-libsy
• cargo test -p switchyard-translation
• commit hooks: cargo fmt, cargo clippy, commitlint

[github-actions]

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