feat: update dependencies and improve caching mechanism

- Added Prometheus client library for metrics collection.
- Refactored garbage collection strategy from random deletion to LRU (Least Recently Used) deletion.
- Introduced per-key locking in cache to prevent race conditions.
- Enhanced logging with structured log messages for cache hits and misses.
- Implemented a retry mechanism for upstream requests with exponential backoff.
- Updated Go modules and indirect dependencies for better compatibility and performance.
- Removed unused sync filesystem implementation.
- Added version initialization to ensure a default version string.

steamcache/steamcache_test.go

@@ -15,9 +15,6 @@ func TestCaching(t *testing.T) {
 
 	sc := New("localhost:8080", "1GB", 10, "1GB", 100, td, "", false)
 
-	sc.dirty = true
-	sc.LogStats()
-
 	if err := sc.vfs.Set("key", []byte("value")); err != nil {
 		t.Errorf("Set failed: %v", err)
 	}
@@ -25,9 +22,6 @@ func TestCaching(t *testing.T) {
 		t.Errorf("Set failed: %v", err)
 	}
 
-	sc.dirty = true
-	sc.LogStats()
-
 	if sc.diskgc.Size() != 17 {
 		t.Errorf("Size failed: got %d, want %d", sc.diskgc.Size(), 17)
 	}