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/gc.go

@@ -4,9 +4,8 @@ import (
 	"runtime/debug"
 	"s1d3sw1ped/SteamCache2/vfs"
 	"s1d3sw1ped/SteamCache2/vfs/cachestate"
+	"sort"
 	"time"
-
-	"golang.org/x/exp/rand"
 )
 
 func init() {
@@ -14,34 +13,30 @@ func init() {
 	debug.SetGCPercent(50)
 }
 
-// RandomGC randomly deletes files until we've reclaimed enough space.
-func randomgc(vfss vfs.VFS, size uint) (uint, uint) {
-	// Randomly delete files until we've reclaimed enough space.
-	random := func(vfss vfs.VFS, stats []*vfs.FileInfo) int64 {
-		randfile := stats[rand.Intn(len(stats))]
-		sz := randfile.Size()
-		err := vfss.Delete(randfile.Name())
-		if err != nil {
-			return 0
-		}
-
-		return sz
-	}
-
+// lruGC deletes files in LRU order until enough space is reclaimed.
+func lruGC(vfss vfs.VFS, size uint) (uint, uint) {
 	deletions := 0
-	targetreclaim := int64(size)
-	var reclaimed int64
+	var reclaimed uint
 
 	stats := vfss.StatAll()
-	for {
-		if reclaimed >= targetreclaim {
+	sort.Slice(stats, func(i, j int) bool {
+		return stats[i].AccessTime().Before(stats[j].AccessTime())
+	})
+
+	for _, s := range stats {
+		sz := uint(s.Size())
+		err := vfss.Delete(s.Name())
+		if err != nil {
+			continue
+		}
+		reclaimed += sz
+		deletions++
+		if reclaimed >= size {
 			break
 		}
-		reclaimed += random(vfss, stats)
-		deletions++
 	}
 
-	return uint(reclaimed), uint(deletions)
+	return reclaimed, uint(deletions)
 }
 
 func cachehandler(fi *vfs.FileInfo, cs cachestate.CacheState) bool {