Refactor golangci-lint configuration and improve error handling

- Updated .golangci.yml to enable default linters and refine suppression rules, enhancing code quality visibility.
- Improved error handling in cmd/root.go by explicitly discarding low-value error messages during fatal exits for consistency with errcheck posture.
- Added best-effort error handling in various locations across the codebase, ensuring that non-critical errors are logged without affecting overall functionality.
- Introduced a new writeMetricsText function to streamline metrics output, improving code clarity and maintainability.

vfs/cache/cache.go

@@ -177,7 +177,7 @@ func (tc *TieredCache) Capacity() int64 {
 
 // promoteToFast promotes a file from slow tier to fast tier
 func (tc *TieredCache) promoteToFast(key string, reader io.ReadCloser) {
-	defer reader.Close()
+	defer func() { _ = reader.Close() }() // best-effort close; error secondary to promotion attempt (async best-effort path)
 
 	// Get file info from slow tier to determine size
 	var size int64
@@ -217,9 +217,10 @@ func (tc *TieredCache) promoteToFast(key string, reader io.ReadCloser) {
 		if vfs, ok := fast.(vfs.VFS); ok {
 			writer, err := vfs.Create(key, size)
 			if err == nil {
-				// Write content to fast tier
-				writer.Write(content)
-				writer.Close()
+				// Write/close errors intentionally discarded: promotion to fast tier is best-effort optimization only.
+				// Failure (e.g. mem pressure, concurrent evict) is non-fatal and does not affect correctness of slow tier.
+				_, _ = writer.Write(content)
+				_ = writer.Close()
 			}
 		}
 	}