- Add configurable vidMap cache size (default: 5 historical snapshots) - Add FilerClientOption struct for clean configuration * GrpcTimeout: default 5 seconds (prevents hanging requests) * UrlPreference: PreferUrl or PreferPublicUrl * CacheSize: number of historical vidMap snapshots (for volume moves) - NewFilerClient uses option struct for better API extensibility - Improved error handling in filerVolumeProvider.LookupVolumeIds: * Distinguish genuine 'not found' from communication failures * Log volumes missing from filer response * Return proper error context with volume count * Document that filer Locations lacks Error field (unlike master) - FilerClient.GetLookupFileIdFunction() handles URL preference automatically - Mount (WFS) creates FilerClient with appropriate options - Benefits for weed mount: * Singleflight: Deduplicates concurrent volume lookups * Cache history: Old volume locations available briefly when volumes move * Configurable cache depth: Tune for different deployment environments * Battle-tested vidMap cache with cache chain * Better concurrency handling with timeout protection * Improved error visibility and debugging - Old filer.LookupFn() kept for backward compatibility - Performance improvement for mount operations with high concurrency