feat: add concurrency support to LRU tests

Introduced conditional compilation for concurrency features in the LRU cache tests. Updated `lru_concurrency.rs` to enable tests only when the "concurrency" feature is active. Modified `lru_integration_test.rs` to conditionally include `ConcurrentLruCache` and its associated tests, enhancing the test suite's flexibility and ensuring it aligns with the concurrency design strategy.

Author: TKorr

tests/lru_concurrency.rs

@@ -1,3 +1,5 @@
+#![cfg(feature = "concurrency")]
+
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::thread;

tests/lru_integration_test.rs

@@ -2,7 +2,9 @@ use std::sync::Arc;
 
 #[cfg(test)]
 mod integration_tests {
-    use cachekit::policy::lru::{ConcurrentLruCache, LruCore};
+    #[cfg(feature = "concurrency")]
+    use cachekit::policy::lru::ConcurrentLruCache;
+    use cachekit::policy::lru::LruCore;
     use cachekit::traits::{CoreCache, LruCacheTrait, MutableCache};
 
     use super::*;
@@ -46,6 +48,7 @@ mod integration_tests {
         println!("✅ Zero-copy LRU core test passed!");
     }
 
+    #[cfg(feature = "concurrency")]
     #[test]
     fn test_concurrent_lru_cache() {
         let cache = ConcurrentLruCache::new(3);
@@ -83,6 +86,7 @@ mod integration_tests {
         println!("✅ Concurrent LRU cache test passed!");
     }
 
+    #[cfg(feature = "concurrency")]
     #[test]
     fn test_database_workload_simulation() {
         // Simulate a database buffer pool workload