v1.13.9 - better Remove errors, short-circuit unsupported fsync, and ReadFull for readfrom

What's Changed

• Backport v2/Client.Remove and File.Sync by @puellanivis in #618
• perf: ensure full write buffer for *File.ReadFrom by @justfalter in #623

New Contributors

• @justfalter made their first contribution in #623

Full Changelog: v1.13.8...v1.13.9