Enhance error handling and metrics tracking in SteamCache

- Introduced a new error handling system with custom error types for better context and clarity in error reporting.
- Implemented URL validation to prevent invalid requests and enhance security.
- Updated cache key generation functions to return errors, improving robustness in handling invalid inputs.
- Added comprehensive metrics tracking for requests, cache hits, misses, and performance metrics, allowing for better monitoring and analysis of the caching system.
- Enhanced logging to include detailed metrics and error information for improved debugging and operational insights.

vfs/vfserror/vfserror.go

@@ -1,7 +1,10 @@
 // vfs/vfserror/vfserror.go
 package vfserror
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 // Common VFS errors
 var (
@@ -9,4 +12,47 @@ var (
 	ErrInvalidKey       = errors.New("vfs: invalid key")
 	ErrAlreadyExists    = errors.New("vfs: key already exists")
 	ErrCapacityExceeded = errors.New("vfs: capacity exceeded")
+	ErrCorruptedFile    = errors.New("vfs: corrupted file")
+	ErrInvalidSize      = errors.New("vfs: invalid size")
+	ErrOperationTimeout = errors.New("vfs: operation timeout")
 )
+
+// VFSError represents a VFS-specific error with context
+type VFSError struct {
+	Op   string // Operation that failed
+	Key  string // Key that caused the error
+	Err  error  // Underlying error
+	Size int64  // Size information if relevant
+}
+
+// Error implements the error interface
+func (e *VFSError) Error() string {
+	if e.Key != "" {
+		return fmt.Sprintf("vfs: %s failed for key %q: %v", e.Op, e.Key, e.Err)
+	}
+	return fmt.Sprintf("vfs: %s failed: %v", e.Op, e.Err)
+}
+
+// Unwrap returns the underlying error
+func (e *VFSError) Unwrap() error {
+	return e.Err
+}
+
+// NewVFSError creates a new VFS error with context
+func NewVFSError(op, key string, err error) *VFSError {
+	return &VFSError{
+		Op:  op,
+		Key: key,
+		Err: err,
+	}
+}
+
+// NewVFSErrorWithSize creates a new VFS error with size context
+func NewVFSErrorWithSize(op, key string, size int64, err error) *VFSError {
+	return &VFSError{
+		Op:   op,
+		Key:  key,
+		Size: size,
+		Err:  err,
+	}
+}