refactor: update function_runner → test_utils cfg gates and docs

Follow-up to dropping the function_runner feature flag.
Gate test_helpers module and function_runner module under test_utils,
and update the doc comment in function_runner.rs accordingly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: naor-starkware

CHANGELOG.md

@@ -14,7 +14,7 @@ Both branches support Stwo prover opcodes (Blake2s, QM31) since v2.0.0.
 
 * refactor: add `CairoFunctionRunner` type alias for `CairoRunner` under the `test_utils` feature flag [#2377](https://github.com/starkware-libs/cairo-vm/pull/2377)
 * refactor: add `function_runner` feature flag and `CairoFunctionRunner` type alias for `CairoRunner` [#2377](https://github.com/starkware-libs/cairo-vm/pull/2377)
-* feat: add `test_helpers` module (`error_utils`, `test_utils`) with `assert_mr_eq!`, `load_cairo_program!` macros and `expect_*` error checkers, behind `function_runner` feature flag [#2378](https://github.com/starkware-libs/cairo-vm/pull/2378)
+* feat: add `test_helpers` module (`error_utils`, `test_utils`) with `assert_mr_eq!`, `load_cairo_program!` macros and `expect_*` error checkers, behind `test_utils` feature flag [#2378](https://github.com/starkware-libs/cairo-vm/pull/2378)
 
 * Add Stwo cairo runner API [#2351](https://github.com/lambdaclass/cairo-vm/pull/2351)
 

vm/src/lib.rs

@@ -26,7 +26,7 @@ pub mod types;
 pub mod utils;
 pub mod vm;
 
-#[cfg(feature = "function_runner")]
+#[cfg(feature = "test_utils")]
 pub mod test_helpers;
 
 // TODO: use `Felt` directly