Update metrics tracking and enhance cache eviction strategies

- Added metrics for bytes saved from cache to improve performance insights.
- Updated cache eviction strategies in MemoryFS and DiskFS to include metrics tracking for hits and evictions.
- Enhanced README.md with updated garbage collection algorithm descriptions and recommendations for cache usage.
- Introduced new madviseSequential functionality for improved memory access hints on Unix systems.
- Adjusted validation configuration in examples to better reflect realistic usage scenarios.

steamcache/steamcache.go

@@ -179,6 +179,17 @@ func New(address string, memorySize string, diskSize string, diskPath, upstream,
 		metrics: metrics.NewMetrics(),
 	}
 
+	// Wire metrics into TieredCache so promotions are counted.
+	c.SetMetrics(sc.metrics)
+
+	// Wire metrics into the concrete storage tiers (MemoryFS / DiskFS) so per-tier hits and evictions are counted.
+	if m != nil {
+		m.SetMetrics(sc.metrics)
+	}
+	if d != nil {
+		d.SetMetrics(sc.metrics)
+	}
+
 	// Wire the request processor (constructor injection of interfaces for the owned wrappers + vfs + client + scalars).
 	// Done after all fields including wrappers are set; before attach goroutines (no impact on lifecycle paths).
 	sc.processor = newRequestProcessor(sc)
@@ -209,12 +220,16 @@ func New(address string, memorySize string, diskSize string, diskPath, upstream,
 		sc.wg.Add(1)
 		go func() {
 			defer sc.wg.Done()
+			t0 := time.Now()
 			_ = d.Size()
 			select {
 			case <-sc.shutdownCh:
 				return
 			default:
 				c.SetSlow(dgc)
+				logger.Logger.Info().
+					Dur("attach_delay", time.Since(t0)).
+					Msg("Disk slow tier attached (mixed mode); prior traffic was memory-only")
 			}
 		}()
 	}