fix: use atomic counter in pet-pipenv test temp dirs to prevent parallel collisions (#408)

The `unique_temp_dir()` helper in pet-pipenv tests used
`SystemTime::now().as_nanos()` to generate temp directory names. On
Windows, `SystemTime` has ~15.6ms resolution, so parallel test threads
can get the same value — causing one test's cleanup (`remove_dir_all`)
to destroy another test's files mid-execution.

**Fix:** Replace the nanos-based name with `process_id + AtomicU64
counter`, which is guaranteed unique across parallel test threads within
the same test binary.

This was observed as a flaky
`detect_pipenv_centralized_env_without_project_file_via_naming_pattern`
failure on Windows CI (e.g., PR #407 CI run).

Author: karthiknadig

crates/pet-pipenv/src/lib.rs

@@ -495,15 +495,15 @@ impl Locator for PipEnv {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::time::{SystemTime, UNIX_EPOCH};
+    use std::sync::atomic::{AtomicU64, Ordering};
+
+    static TEST_DIR_COUNTER: AtomicU64 = AtomicU64::new(0);
 
     fn unique_temp_dir() -> PathBuf {
         let mut dir = std::env::temp_dir();
-        let nanos = SystemTime::now()
-            .duration_since(UNIX_EPOCH)
-            .unwrap()
-            .as_nanos();
-        dir.push(format!("pet_pipenv_test_{}", nanos));
+        let id = std::process::id();
+        let counter = TEST_DIR_COUNTER.fetch_add(1, Ordering::Relaxed);
+        dir.push(format!("pet_pipenv_test_{}_{}", id, counter));
         dir
     }