ci: Stabilize flaky ttl_evicts_even_with_frequent_access test in tiles_test (#2715)

- [x] Reproduce `ttl_evicts_even_with_frequent_access` failure multiple
times in `-p martin-core --test tiles_test`
- [x] Identify root cause in test/cache timing behavior and define
minimal fix
- [x] Implement minimal code/test change to remove flakiness
- [x] Re-run targeted tests multiple times to confirm the flake is fixed
- [x] Run broader relevant martin-core cache tests to guard regressions
- [x] Run parallel validation (code review + CodeQL)
- [x] Create pull request

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: CommanderStorm <26258709+CommanderStorm@users.noreply.github.com>

Author: Copilot

martin-core/tests/tiles_test.rs

@@ -37,18 +37,22 @@ async fn cache_entry_evicted_after_ttl_expires() {
 #[tokio::test]
 async fn ttl_evicts_even_with_frequent_access() {
     // TTL evicts entries regardless of access pattern (unlike TTI)
-    let ttl = Duration::from_millis(80);
+    let ttl = Duration::from_millis(200);
     let cache = TileCache::new(CACHE_SIZE, Some(ttl), None);
 
     insert(&cache, "src", ORIGIN, None, b"data").await;
 
     // Access repeatedly — this should NOT extend the TTL
     for _ in 0..3 {
-        tokio::time::sleep(Duration::from_millis(20)).await;
+        tokio::time::sleep(Duration::from_millis(30)).await;
         assert_hit(&cache, "src", ORIGIN).await;
     }
 
-    wait_and_flush(&cache, Duration::from_millis(30)).await;
+    // Still before TTL expiration.
+    tokio::time::sleep(Duration::from_millis(60)).await;
+    assert_hit(&cache, "src", ORIGIN).await;
+
+    wait_and_flush(&cache, Duration::from_millis(80)).await;
 
     assert_miss(&cache, "src", ORIGIN, None, b"new").await;
 }