Optimizing network programming: Zero-copy and `io.ReaderFrom`.

Zero-copy techniques minimize copying data between kernel and user space, vastly improving I/O performance.

When transferring data from a file to a network socket, standard copying reads data into Go user-space RAM, then writes it back to the kernel socket. The io.Copy function smartly checks if types implement io.ReaderFrom or io.WriterTo. If supported (like TCP sockets), Go utilizes the sendfile Linux syscall, moving data directly within the kernel, saving CPU.