fix(audit): treat *_fixture(s).rs as test paths in is_test_path

Shared test-fixture modules like src/commands/trace/test_fixture.rs are
declared `#[cfg(test)] mod test_fixture;` and consumed only by sibling
*_tests.rs files, but is_test_path did not recognize them — it matched
_test.rs / _tests.rs / test.rs / tests.rs but not *_fixture(s).rs. As a
result the fixture's setup code (fs writes, git process spawns to build
scenarios) was scanned as production command code and flagged by the
thin_command_adapter detector.

Extend is_test_path filename detection to cover `*_fixture.rs` and
`*_fixtures.rs`. This is precise: test_fixture.rs ends with _fixture.rs
and is now excluded, while the existing negative case test_helpers.rs
(deliberately NOT a test path) is preserved.

Resolves #8335.

Author: chubes4

src/core/code_audit/walker.rs

@@ -132,9 +132,14 @@ pub fn is_test_path(relative_path: &str) -> bool {
     let file_name = relative_path.rsplit('/').next().unwrap_or(relative_path);
 
     // Rust: foo_test.rs, foo_tests.rs, and bare test.rs / tests.rs modules
-    // (conventionally wired as `#[cfg(test)] mod tests;`).
+    // (conventionally wired as `#[cfg(test)] mod tests;`). Also cover shared
+    // test-fixture modules — `*_fixture(s).rs` (e.g. test_fixture.rs) — which are
+    // conventionally `#[cfg(test)] mod` fixtures consumed by sibling `*_tests.rs`
+    // files, not production code.
     if file_name.ends_with("_test.rs")
         || file_name.ends_with("_tests.rs")
+        || file_name.ends_with("_fixture.rs")
+        || file_name.ends_with("_fixtures.rs")
         || file_name == "test.rs"
         || file_name == "tests.rs"
     {
@@ -219,6 +224,10 @@ mod tests {
         // Bare `tests.rs` / `test.rs` modules (conventionally `#[cfg(test)] mod tests;`).
         assert!(is_test_path("src/commands/bench/tests.rs"));
         assert!(is_test_path("src/core/triage/test.rs"));
+        // Shared `*_fixture(s).rs` test-support modules (conventionally
+        // `#[cfg(test)] mod test_fixture;`), consumed by sibling `*_tests.rs`.
+        assert!(is_test_path("src/commands/trace/test_fixture.rs"));
+        assert!(is_test_path("src/core/runner/exec_fixtures.rs"));
     }
 
     #[test]