v0.2.1

• (breaking) @fs.File::read now returns the number of bytes, data length becomes an optional argument
• (breaking) data length argument of @fs.File::write is now an optional argument
• add optional offset to @fs.File::read and @fs.File::write
• @fs.File::write now ensures all data are written
• add @async.spawn_loop API with automatic retry
• add file size and file seeking API to @fs.File
• add keep alive support to @socket.TCP
• adapt to latest MoonBit release (2025-07-22)
• bugfix