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.

vfs/disk/disk_madvise_unix.go

@@ -0,0 +1,13 @@
+//go:build !windows
+
+package disk
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+// madviseSequential gives the OS a hint that the memory region will be
+// accessed sequentially. This is a no-op or best-effort on some platforms.
+func madviseSequential(b []byte) error {
+	return unix.Madvise(b, unix.MADV_SEQUENTIAL)
+}